Refactored TripleStore, splitting the code into subclasses for each type of triplestore supported.

In addition, re-added support for using curl when up/downloading large
triple sets from HTTP stores, and added support for reading
RDFLib-based stores entirely into memory, which speeds up queries.

Squashed commit of the following:

commit 32016d0a68661dfc69d542f83f0939446c6f5f93
Author: Staffan Malmgren <staffan.malmgren@gmail.com>
Date:   Fri Aug 2 08:18:30 2013 +0200

    final doc work on this feature

commit 00aaf9c995e9b5d6dd2be8370992165b221a9dc2
Author: Staffan Malmgren <staffan.malmgren@gmail.com>
Date:   Fri Aug 2 01:58:21 2013 +0200

    Made documentrepository.generate actually use the new inmemory support when available. Queries that used to take 12 sec now takes 5, so improvements, but still too slow for practical use

commit 3f31fe918a7105810ab310972bfbb39df680eed6
Author: Staffan Malmgren <staffan.malmgren@gmail.com>
Date:   Fri Aug 2 01:44:05 2013 +0200

    support for curl for RemoteStore classes, made all failing test cases pass. Feature mainly done, just cleanup doc work left

commit e704bb300518af6cd62e95e5875fc1a77d7de712
Author: Staffan Malmgren <staffan.malmgren@gmail.com>
Date:   Thu Aug 1 21:07:22 2013 +0200

    refactored all of triplestore, added inmemory support for rdflib backends
The WSGI app now supports content negotiation for documents in repositories

Squashed commit of the following:

commit 969f902c9b67a50afb9c3fdee4435eadd80e7f4c
Author: Staffan Malmgren <staffan.malmgren@gmail.com>
Date:   Fri Aug 2 15:24:53 2013 +0200

    fixed weird setlocale bug for py2, moved README from markdown back to reST

commit a19b01b8013d8b9ceb2499abd5225027f7442763
Author: Staffan Malmgren <staffan.malmgren@gmail.com>
Date:   Fri Aug 2 14:47:35 2013 +0200

    basic conneg tests work (only json-ld output is missing)

commit 32491936c018da380674be54bdbfb0b2318d2859
Author: Staffan Malmgren <staffan.malmgren@gmail.com>
Date:   Fri Aug 2 11:00:55 2013 +0200

    first steps of testcase harness for content negotiation tests
Final release prep
onwards to the next release...