Add JsonPath library to request fields from api

To get commit hash, version, author and all this
from your api now you can specify which json
field you want to get that information from your
json api response using jsonpath field notation
see more at https://code.google.com/p/jsonpath/wiki/PHP
http://goessner.net/articles/JsonPath/
Make it optional to specify a version field
Merge pull request #3 from leibowitz/add_json_path_fields

Add JsonPath library to request fields from api