Substituting rdfstore with rdflib to fix, fix #1

[nicola]

Attention: This is a breaking change since it supports a different callback style (the way it should be).

This change does the following:

1. Different callback style

   agent.verify(function(err, callback) { .. })
   

   instead of

   agent.verify(function(success) { .. }, function(fail) { .. })
   

2. Removing coffee-script (all written in plain javascript)

3. Removed unused dependencies and updated the current ones (rdfstore has currently a bug that I reported store.load not working antoniogarrote/rdfstore-js#98 and fixed Fixing batchLoad if condition #98 antoniogarrote/rdfstore-js#99, however it is not merged yet, hence making the stability of this package questionable. We should implement it with rdflib instead)

4. Tests

5. Adding travis

6. Removing rdfstore and using rdflib instead

7. Changing the APIs, so we now just need

   var webid = require('webid')
   webid.verify(cert, function(err, uri) {
   })
   

   as in the Readme.md