Allow check-in notes to be set on the command line

New command line switches for rcheckin:
-c, --code-reviewer=VALUE  Set code reviewer
                             e.g. -c "John Smith"
-s, --security-reviewer=VALUE
                           Set security reviewer
                             e.g. -s "John Smith"
-p, --performance-reviewer=VALUE
                           Set performance reviewer
                             e.g. -p "John Smith"
Support for security and performance reviewer

The following directives are supported from a commit message for
specifying checkin notes:
git-tfs-code-reviewer: John Smith
git-tfs-security-reviewer: John Smith
git-tfs-performance-reviewer: John Smith
Optional spaces in commit message directives

Previously you needed at least one space after the directive, this is
now optional. For associating with work items the space between the
number and the action is also optional.

Examples:
git-tfs-work-item: 1234 associate

Can now be specified as:
git-tfs-work-item:1234 associate

Or if you are really lazy:
git-tfs-work-item:1234associate

Same for other directives:
git-tfs-code-reviewer:John Smith
Unit test for getting reviewers from message