Fix parsing of gzipped distant files

[gmetais]

Hi!

Analyze-css fails to parse some files when they are compressed.

Some servers are misconfigured, they always return compressed content, even if the request doesn't contain the Accept-Encoding header. This leads to problems with analyze-css, which is not able to ungzip these files.

Example:

$ analyze-css --url=http://cdn.quilt.janrain.com/2.2.19/providers.css

"offenders": {
    "parsingErrors": [
      "missing '}' @ 1:120",
      "property missing ':' @ 1:125",
      "missing '}' @ 1:125",
      "property missing ':' @ 1:306",
      "missing '}' @ 1:306",
      "property missing ':' @ 2:226",
      "missing '}' @ 2:226",
      "missing '}' @ 2:305",
      "missing '}' @ 2:577",
      "missing '}' @ 3:24",
      "selector missing @ 3:24"
    ]
  }

While downloading the file and running a local test using --file instead of --url works without any parsing errors.

The fix adds compatibility with gzip and deflate to analyze-css.

I have also taken the liberty to add an Accept-Encoding:gzip, deflate header to the requests, to save a little bandwidth and speed-up analyze-css.

[macbre]

Thanks for the fix! I guess the long term solution is to use a request like library for handling HTTP requests.

[macbre]

See #120