revision to documentation
small fixes, added label
YCMInternal: fix variable name
YCMInternal: Use string(MAKE_C_IDENTIFIER) instead of several string(REGEX REPLACE)
YCMInternal: strip path from internal file names
YCMInternal: Use a more explicative filename when more than one file is installed
YCMInternal: string(MAKE_C_IDENTIFIER) is not available on CMake < 2.8.12
YCMInternal: Better handling of the _clean_filename cases
YCMInternal: Use string(MAKE_C_IDENTIFIER) if available
YCMInternal: Quote filename to avoid issues
YCMInternal: Prepend hash with underscore

This allows us to have a similar name in all the cases, since later
an underscore is added if the name starts with [0-9] but it is not when
it starts with [a-f]
YCMInternal: Quote filenames everywhere to avoid possible issues
YCMInternal: Add empty command to make Xcode happy

Fix #63