More lenient config files syntax

[jawshooah]

Fix the issue of JSON config files not working with more than one option specified (#567).

Also allow JSON config values to be strings rather than arrays, e.g.

{
    "format": "checkstyle-xml",
    "ignore": "important"
}

Finally, and perhaps most significantly, traditionally formatted .csslintrc files may now have arbitrary whitespace! So this also addresses #359. The following is now perfectly valid:

--ignore=
  adjoining-classes,
  box-model,
  compatible-vendor-prefixes,
  duplicate-background-images,
  import,
  important,
  outline-none,
  overqualified-elements,
  text-indent
--warnings=
  gradients,
  font-sizes,
  floats
--errors=
  shorthand,
  universal-selector,
  fallback-colors
--format=checkstyle-xml

[bwinton]

I believe it’s more efficient to use /[\s\n\r]+/g instead of /[\s\n\r]/g, because then the replacement happens only once for each run of whitespace, instead of once for every character of whitespace.

Also, MDN says that \s includes both \n and \r, so you could simplify it further to /\s+/g. :)

[jawshooah]

Addressed in f7f43e0.

[XhmikosR]

@jawshooah: please take care of @bwinton's comments.

[jawshooah]

@XhmikosR done. Was going to add tests, but I don't really see a natural place to put them...

[XhmikosR]

@jawshooah: can you squash the patches into one? If not I'll merge it manually another time.

[jawshooah]

Will do. I'm not familiar with the layout of the tests in this repo; can you think of a place where it would make sense to add tests for reading config data?

[jawshooah]

@XhmikosR squashed.