[#118] Adding version info to Twgit Tool

The version info will look for every files specified in the
TWGIT_VERSION_INFO_PATH to replace Id tag with starting new tag.
The Id tag has to be written either as '$Id$' or '$Id:1.2.3'
When beginning a new tag (twgit init, twgit release start or
twgit hotfix start), the value will be updated with new version
information (ex. $Id:1.3.0$).

Specific tests have been written to check that waited and
unwaited substitution are correctly performed for the three way
of starting a new tag.