TortoiseGitMerge: Add Mark block and Use left file except marked blocks

This facilities partial commit (Restore after commit in TortoiseGit).
Based on TortoiseSVN revision 25282-25285.

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Document the new "mark block" feature

Based on TortoiseSVN revision 25288, 25290

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Fixed issue #2134: Easier to select lines to partial commit in TortoiseGitMerge

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Add the override keyword

Based on TortoiseSVN revision 25291

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>