Add support for .checkbuildrc

[ruimarinho]

Following the convention of most projects, including the ones that this lib makes use of, I think the main checkbuild configuration file should include the rc suffix.

Therefore, I propose renaming .checkbuild to .checkbuildrc as the standard config file. The old name is still supported, so backwards compatibility is guaranteed.

[FGRibreau]

If we are going to rename .checkbuild to .checkbuildrc we may want to rename check-build cli to checkbuild as well, what do you think?

[ruimarinho]

That would be interesting - jshint, jslint, jscs are single keywords too, so the dash is a bit out of place :) however, I'd recommend doing that separately as version 2.0 because it is a BC break.

[FGRibreau]

That's definitely what I had in mind :)