Add sum as backend requirement

Summing is now several orders of magnitude faster for both CSMat and ScipySparseMat.
Add convertVectorToDense to sparse backends

Used in _conv_to_np, allows more efficient use of ScipySparseMat when iterating over rows/cols
Add docstrings to scipysparse module
Fix issue with iteration of length 1 dimension

Added more unit tests here, as this was caught in QIIME's unit tests.
Add 1x1 special case test to _conv_to_np tests
Add more sum tests

Fix scipy code to handle special case where result should be 1x1 instead of scalar.
Add CSMat.convertVectorToDense tests
Add CSMat.sum tests
Slight performance improvements to vector convert
Add basic unit test for ScipySparseMat

Still need to add tests for more complex methods.
Add convert and transpose tests

Also fixed a bug in transpose (when in lil format) that was unearthed by these tests. Good thing we're unit testing!