An alternative constant _size_constant is provided for use in C++98,
for example for declaring arrays.
Also renamed underlying_traits to integral_mapping.
The documentation is now generated from markdown. Samples are generated from the
tutorial pages. Testing is done by a Python script which runs the tests for a
large number of compilers.
This version is not very developer-friendly - the Python scripts need ways of
limiting what compilers they try to run. If you don't have 15 compilers
installed, you won't be able to run the tests in this commit. Fix coming soon.
