Began work on triangle "batches"

- added TriangleBatch type and supporting code to make more effective use of
  SIMD registers
- fixed typo in README
- added pretty-printer for SIMD wrapper classes in python-gdb.py
Triangle batches now work

However, the ray tracer is now slightly slower. The k-d tree builder needs to be
retuned.
*Now* the ray tracer is consistently faster

- the k-d tree builder's parameters can now be supplied by the user
- the tracern modules can be built with a ray tracer that doesn't accept
  primitive batch objects (in case SIMD support is not available)
- generate_simd.py no longer leaves an incomplete file when an error occurs
Completed the Python interface to the new classes

also:
- fixed segmentation fault triggered by incorrect arguments to certain classes
- updated documentation
- updated test script to work again and added new test