blame-options.txt: also mention 'funcname' in '-L' description

blame-options.txt: also mention 'funcname' in '-L' description

Make it clearer that a function can be blamed by feeding `git blame`
'-L :<funcname>' by mentioning it at the beginnning of the description
of the '-L' option.

Also, in 'line-range-options.txt', which is used for git-log(1) and
gitk(1), do not parenthesize the mention of the ':<funcname>' mode, to
place it on equal footing with the '<start>,<end>' mode.

Signed-off-by: Philippe Blain <redacted>
Signed-off-by: Junio C Hamano <redacted>