Merge will fix #4, close #5, and also improves DESCRIPTION file

Contains the following changes:
* Changes from ```httr::guess_media()``` to ```mime::guess_type()```
* Added URL and BugReport to DESCRIPTION file
* Better documenation, in line with [package documentation](http://r-pkgs.had.co.nz/description.html)
* Version number is moved to 1.4.1