Twittersearch

* added support for user-defined callback-method while performing API queries (issue 25)
* added support for advanced query operators (issue 24)
* adjusted search term parsing in method TwitterSearchOrder.set_search_url()
* auto-handling of keywords with spaces

* PEP-8 compatible API (issue 12)
* added support of loading timelines of users
* simplified proxy functionality (no usage of dicts but plain strings)
* simplified geo-code parameter (``TwitterSearchOrder.set_geocode(...,metric=True)`` renamed to ``set_geocode(...,imperial_metric=True)``)
* simplified ``TwitterSearch.get_statistics()`` from dict to tuple style (``{'queries':<int>, 'tweets':<int>}`` to ``(<int>,<int>)``)
* dropped Python 2.6 support (it still works, but some test cases are failing and it's just too much work to add support for 2.6 + 2.7 + 3.x)
* Full rewrite of documentation

* Fixed codec error on Win7 installation (issue 21)
* Added manual iteration support (issue 20)

* fixed proxy usage at initialization of TwitterSearch object

* fixed missing url encoding of search keywords (issue 16)
* created test to check url encoding of keywords
* fixed typo in documentation (issue 17)

* fixed a bug (issue 10): min() with lambda-function doesn't work with empty responses