* Makes compiler output much more readable
This is configurateable through CONTINUABLE_WITH_IMMEDIATE_TYPES,
and automatically enabled for debug builds but disabled
for release builds.
* Remove the old continuable-trait.hpp header
* Make the signature of continuable not dependent anymore
on any size of the arguments which fixes the compilation
with forward declared types.
Thanks Rogiel for the correspoding bug report.
Closes#11
