Update class to install and manage git on RedHat family.
Fix documentation and remove debug.
Add perl-Error and epel dependencies

Without perl-Error from epel, the command 'git add -p' fails:

Can't locate Error.pm in @INC (@INC contains:
/usr/share/perl5
/usr/local/lib64/perl5
/usr/local/share/perl5
/usr/lib64/perl5/vendor_perl
/usr/share/perl5/vendor_perl
/usr/lib64/perl5 .)
at /usr/share/perl5/vendor_perl/Git.pm line 101.
BEGIN failed--compilation aborted at /usr/share/perl5/vendor_perl/Git.pm
line 101.
Compilation failed in require at
/usr/libexec/git-core/git-add--interactive line 7.
BEGIN failed--compilation aborted at
/usr/libexec/git-core/git-add--interactive line 7.
Add spec testing.
Fix inconsistencies in README.
Merge pull request #3 from nanliu/readme

Update git module