Small API change -- tokenize_and_recognize takes string_piece...

instead of const char*. This is a consequence of MorphoDiTa
change 5493e650 and avoids needless allocation in case we perform
tokenize_and_recognize on paragraphs only (as in the web service).

The changes does not affect bindings or existing source code.
Convert CR LF line endings to LF only.
Fix warning in clang++.
Add clang 3.2+ to list of supported compilers.
Bump version to 0.93, add CHANGES file, update documentation.