H in gr* aliases (git reset) means --hard

Principle is to use a capital letter for more dangerous
commands. grh means "git reset HEAD", which cannot involve data lose.
grH means "git reset --hard", which CAN involve data lose.
grhH now means "git reset --hard HEAD".

I intentionnaly chose to not aliase H to "HEAD" and h to --hard.

Signed-off-by: Gaetan Semet <gaetan@xeberon.net>