add -F/--fixed-strings as alias for -Q/--literal

-F is compatible with POSIX grep(1)
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html

--fixed-strings is compatible with GNU grep(1)
https://www.gnu.org/software/grep/manual/grep.html#grep-Programs

This is the most annoying (to me) muscle-memory difference from grep.
document -F/--fixed-strings
add bash completion for -F/--fixed-strings
Improve logging for skipping ignore file and Git excludesfile
Use `--path` with `git config` to get the resolved excludesfile

Fixes https://github.com/ggreer/the_silver_searcher/issues/159
Allow unlimited depth.

Add option --depth=-1 for unlimited search depth.
Fix arguments to `log_debug` in `path_ignore_search`
Merge pull request #548 from blueyed/debug-fix-args

Fix arguments to `log_debug` in `path_ignore_search`
Merge branch 'dash-F' of git://github.com/jpouellet/the_silver_searcher into jpouellet-dash-F

Conflicts:
	src/options.c
Merge branch 'jpouellet-dash-F'

Conflicts:
	src/options.c
Merge pull request #539 from kevinxucs/max-depth

Allow unlimited depth.
Merge pull request #537 from blueyed/fix-git-excludesfile-expand

Expand core.excludesfile setting from "git config"
Document --[no-]recurse

Both options are already covered by Bash completion.