Consolidated pull requests preparing for 0.2.0

With this branch I'm trying to merge the various open pull requests to support an official 0.1.1  release in the not too distant future.

**What I've done to this branch so far:**
1. Merged my commits from #20 (MBTiles) which fix issues https://github.com/mapbox/mbxmapkit/issues/3 and https://github.com/mapbox/mbxmapkit/issues/7
2. Merged my branch for https://github.com/mapbox/mbxmapkit/pull/21 (Maki markers & simplestyle) which fixes issues https://github.com/mapbox/mbxmapkit/issues/5 and https://github.com/mapbox/mbxmapkit/issues/9. This had some conflicts with the MBTiles code, so I resolved that stuff.
3. Merged my branch for https://github.com/mapbox/mbxmapkit/pull/23 (cache stuff) which fixes issue https://github.com/mapbox/mbxmapkit/issues/22
4. Merged @jparise's branch for https://github.com/mapbox/mbxmapkit/pull/27 (image quality api)

~~**My present todo list:**~~
~~1. Figure out what's going on with the podspec (see https://github.com/mapbox/mbxmapkit/issues/34) and get it working, ideally including the correct stuff for libsqlite3 so that the ifdef's can be removed from the MBTiles code~~ **Update:** see https://github.com/mapbox/mbxmapkit/issues/34#issuecomment-35360038
~~2. Finish my branch for overzooming. So far I've got it working for MBTiles on iOS, as I described at  https://github.com/mapbox/mbxmapkit/pull/20#issuecomment-34540499, but I also need to get it working for online tiles (see https://github.com/mapbox/mbxmapkit/issues/35).~~ **Update:** see #42
~~3. Figure out if my branch for https://github.com/mapbox/mbxmapkit/pull/31, which addresses issue https://github.com/mapbox/mbxmapkit/issues/26 (crashing during rendering) works. I never finished testing it because it needs a more complicated sample app to fully reproduce the problem.~~ **Update:** see #26 
~~4. Re-work the existing sample apps, or perhaps add more build targets, for the purpose of demonstrating how to use the various new features.~~ **Update:** see #43 
~~5. Test all this stuff to make sure it compiles and works properly on both iOS and MacOS. In particular, there's a real good chance that the image manipulation code for overzooming will need changes to compile on OS X.~~ **Update:** see #40 
~~6. Update the documentation and maybe write a tutorial or two.~~ **Update:** see #41