refactoring, integration with xctool, various improvements

- optimized performance by not constructing the whole json compilation database in memory
- added support for logs coming from xctool's json-reporter
- refactored code using a tokenizer (shlex for -rare- complicated cases, a simple 'split' otherwise)
- made ObjectiveC implicit headers explicit
- made .pth recovery work also for .h source files
- moved top-level into main() for better style
update pull request after discussion
Merge from matbd/master
Support .pch.pch to accommodate Xcode 5 DP
Added a few tests
Merge pull request #1 from lqi/matbd-master

Changes to Accommodate Xcode 5 DP and A Few Tests
Merge pull request #7 from matbd/master

Heavy refactoring, integration with xctool, various improvements