Switch to taped blocked reverse mode, seems around 2x faster
tests: test also sparse formats
Makefile: better test handling
Implement tape processing for the sparse formats
Update examples and README
Initial work on explicit elemental operations
Add elementwise operations
Add scalar-matrix and scalar-vector operations
Switch back to forward-mode, but with external storage
Keep track of taylor premultiplier, to avoid having to copy data on multiplication/const. summation