GM test - add git_revision to list of generators
git_revision generator impl
VFW and GF - more tests for greater code coverage
VFW: check_unexpected_options_properties --rename--> check_no_extra_options_properties
JsonCreator - test generates correct output
git_revision - bug fix result --> result.stdout
git_revision - label string 'git_version' --> 'git_revision' for consistency
VFW bug fix - 'this' to 'that'
git_revision --> git_describe (for clarity)
grunt_version_file - git_describe added as a default generator
VFW - grunt.file.write is sync by default
README.md - updated for version 0.2.0
v0.2.0 bump