script: new create-table script.

I wanted to add new tables for which I could find no listing anywhere,
even though iconv has support for it (not core Python though), which are
GEORGIAN-ACADEMY and GEORGIAN-PS.
I could find info on these in libiconv source (./lib/georgian_academy.h
and ./lib/georgian_ps.h), though rather than trying to read these, I
thought I should just do the other way around: get back a table from the
return value of iconv API (or Python decode() when relevant).

So this script is able to generate tables in the format used under
script/charsets/, from either Python decode() or iconv. It will be much
useful!

script/create-table.py

@@ -0,0 +1,137 @@
+#!/bin/python3
+# -*- coding: utf-8 -*-
+
+# ##### BEGIN LICENSE BLOCK #####
+# Version: MPL 1.1/GPL 2.0/LGPL 2.1
+#
+# The contents of this file are subject to the Mozilla Public License Version
+# 1.1 (the "License"); you may not use this file except in compliance with
+# the License. You may obtain a copy of the License at
+# http://www.mozilla.org/MPL/
+#
+# Software distributed under the License is distributed on an "AS IS" basis,
+# WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+# for the specific language governing rights and limitations under the
+# License.
+#
+# The Original Code is Mozilla Universal charset detector code.
+#
+# The Initial Developer of the Original Code is
+# Netscape Communications Corporation.
+# Portions created by the Initial Developer are Copyright (C) 2001
+# the Initial Developer. All Rights Reserved.
+#
+# Contributor(s):
+#          Jehan <jehan@girinstud.io>
+#
+# Alternatively, the contents of this file may be used under the terms of
+# either the GNU General Public License Version 2 or later (the "GPL"), or
+# the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+# in which case the provisions of the GPL or the LGPL are applicable instead
+# of those above. If you wish to allow use of your version of this file only
+# under the terms of either the GPL or the LGPL, and not to allow others to
+# use your version of this file under the terms of the MPL, indicate your
+# decision by deleting the provisions above and replace them with the notice
+# and other provisions required by the GPL or the LGPL. If you do not delete
+# the provisions above, a recipient may use your version of this file under
+# the terms of any one of the MPL, the GPL or the LGPL.
+#
+# ##### END LICENSE BLOCK #####
+
+import optparse
+import os
+import subprocess
+import sys
+
+script_path = os.path.relpath(__file__)
+
+usage = 'Usage: {} <CHARSET-NAME>\n' \
+        '\nEx: `{} ISO-8859-15`'.format(script_path, script_path)
+
+description = "Internal tool to generate a charset table."
+cmdline = optparse.OptionParser(usage, description = description)
+(options, charset) = cmdline.parse_args()
+if len(charset) != 1:
+  sys.stderr.write("Please choose exactly one charset as argument.\n")
+  exit(1)
+
+charset = charset[0]
+
+use_iconv = False
+try:
+  b' '.decode(charset)
+except LookupError:
+  use_iconv = True
+
+def get_utf8_char(bchar, charset, iconv):
+  if iconv:
+    try:
+      call = subprocess.Popen(['iconv', '-f', charset, '-t', 'UTF-8'],
+                               stdin=subprocess.PIPE, stdout=subprocess.PIPE,
+                               stderr=subprocess.DEVNULL)
+      if call.poll() is not None:
+        (_, error) = call.communicate(input='')
+        sys.stderr.write('Error: `iconv` ended with error "{}".\n'.format(error))
+        exit(1)
+      (uchar, _) = call.communicate(input=bchar)
+    except FileNotFoundError:
+      sys.stderr.write('Error: `iconv` is not installed.\n')
+      exit(1)
+    if len(uchar) > 0:
+      return uchar.decode('UTF-8')
+    else:
+      return None
+  else:
+    try:
+      return bchar.decode(charset)
+    except UnicodeDecodeError:
+      # Typical error:
+      # UnicodeDecodeError: 'charmap' codec can't decode byte 0x81 in position 0: character maps to <undefined>
+      # It would mean an illegal character.
+      return None
+
+print('## Table generated by {} with {} ##'.format(script_path, 'iconv' if use_iconv else 'Python decode()'))
+
+print('# X0  X1  X2  X3  X4  X5  X6  X7  X8  X9  XA  XB  XC  XD  XE  XF   #')
+print('charmap = \\')
+sys.stdout.write('[')
+for l in range(0x10):
+  sys.stdout.write('\n  ')
+  has_printable = False
+  for c in range(0x10):
+    char = bytes([c + l * 0x10])
+    char = get_utf8_char(char, charset, use_iconv)
+    if char is None:
+      sys.stdout.write('ILL,')
+    elif char.isalpha():
+      sys.stdout.write('LET,')
+      has_printable = True
+    elif char.isdigit():
+      sys.stdout.write('NUM,')
+      has_printable = True
+    elif char == '\n' or char == '\r':
+      sys.stdout.write('RET,')
+    elif char.isprintable():
+      sys.stdout.write('SYM,')
+      has_printable = True
+    else:
+      sys.stdout.write('CTR,')
+
+  sys.stdout.write(' # {}X'.format(hex(l)[-1:].upper()))
+
+  if has_printable:
+    sys.stdout.write('\n #')
+    # The line has at least one printable character. Print in comment for
+    # debugging.
+    for c in range(0x10):
+      char = bytes([c + l * 0x10])
+      char = get_utf8_char(char, charset, use_iconv)
+      if char is None:
+        sys.stdout.write('ILL ')
+      elif char == '\n' or char == '\r':
+        sys.stdout.write('RET ')
+      elif char.isalpha() or char.isdigit() or char.isprintable():
+        sys.stdout.write("'{}' ".format(char))
+      else:
+        sys.stdout.write('CTR ')
+sys.stdout.write('\n]')