search: Adjust log levels for max search depth

When a user has specified a specific max search depth (--depth), it is
reasonable to assume that they are aware of it. In this case, it should
suffice to output this information on the debug level.

Relatedly, it is not (in my opinion) an error to exceed the max search
depth, since the program is designed that way. I've lowered it to a
warning.

This increases, in my experience, the user friendliness of the --depth
option, since it outputs a lot less noise.
Fix test case. Somebody forgot to sort this.
Add -H as short option for --heading
 Add --null option to provide input to 'xargs -0'
 Update man page with --null option.
Adds .less filetype option
Fix lame issue where results can be in a different order depending on random stuff.
Add Travis CI status to README.
Merge pull request #480 from barraponto/less-file-type

Adds .less filetype option
Fix barraponto's broken test case.
Merge branch 'master' into single_file_heading
Merge pull request #477 from ajwans/null

 Add --null option to provide input to 'xargs -0'
Better path printing logic. This lets --heading and --noheading work with single files. Still need to fix some issues with --parallel though.
Add another print option to fix --parallel. This seems ready to merge.
Merge pull request #484 from ggreer/single_file_heading

Single file heading
Use NUL on windows instead of /dev/null
Merge pull request #486 from larsch/win32-dev-null

Use NUL on windows instead of /dev/null
Added support for ClojureScript (.cljs) and Leniningen's cljx cross-compiler (.cljx) to --clojure
List all files on `ag -l` without arguments
Merge pull request #491 from gfxmonk/list_noquery

List all files on `ag -l` without arguments