BaseTools/Scripts: Allow GitHub ID at end Maintainers.txt lines

BaseTools/Scripts: Allow GitHub ID at end Maintainers.txt lines

* Update GetMaintainer.py to support an optional GitHub ID at the
  end of maintainer and reviewer lines.
* Remove contents after email address from standard output
* Fix minor issue in --lookup to convert file path separators
  from '\' to '/' to be compatible with regular expression
  file matching.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Cc: Yuwei Chen <yuwei.chen@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>