Imp usage of assert_equald and assert _true
Imp parameter renaming
Imp all_finite test can now be skipped
Imp sparse support
Imp new fit function
Imp new dense mean function
Imp new sparse mean function using data, indices and indptr
Fix sparse iterator
Add fill_value
Del unnecessary output
Imp median tests
Imp sparse mean and medians
Imp move bottleneck sparse mean code into a separate function for profiling
Imp sparse mean and sparse median speed
Imp refactoring + comments
Del old code
Imp comments + functions and parameters naming
Imp comments + refactoring + del prints
Add some new tests + support of empty columns