Assume Ruby Files for parser

To simplify our lives, let's assume that files are Ruby if they aren't recognized by any other parser (for now, that's just .erb). This will eliminate encountering "unknown file type" errors.

If assuming Ruby fails, we'll have to encourage people to use the include / exclude globs in their configs to handle other types of files.

We could assume a file without an extension is an executable, check to see if it looks like a Ruby executable, and ignore it if it's not. @thegedge prefers being explicit, but can understand that a larger repo may have built up a lot of executable files, many of which may not be Ruby.

Start by locating the parser dispatch and the handling that produces "unknown file type" errors. Check how .erb and extensionless files are classified, then add coverage showing that otherwise-unrecognized files are treated as Ruby and that non-Ruby executables are handled as described; done means these files no longer produce unknown-type errors.