Development

I made some misc changes. The major ones are:
- Replaced jquery with cheerio - see #3 .
- Added fileType helper to detect images by their file headers (instead of using the extension; atm just used in jpgmin for testing purposes though I have tested it so far with some folders containing misc files - working fine so far) - related to #30 
- Added pathFromSrc helper that fixes #9 - currently implemented in the processImageFiles and the inlineImg task (fixing the unused dest option)


@LaurentGoderre you still pull request your additions for others to sign it I guess? If thats the appropriate behavior let me know so I'll start doing the same :)