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.
Add swift filetype option
Alphabetize filetype options
Merge pull request #472 from neilpa/filetypes-swift

Add Swift file type
Rename max to ag_max. Fixes #469
Case insensitive matching is now the default, reflect that in the docs
Merge pull request #474 from Pyrohh/master

Case insensitive matching is now the default, reflect that in the docs
Fix test case. Somebody forgot to sort this.
Add -H as short option for --heading
Fix test case. Somebody forgot to sort this.
 Add --null option to provide input to 'xargs -0'
 Update man page with --null option.
Adds .less filetype option
Initial Travis-CI config
Use sudo in travis build steps.
Disable failing test for now.
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.