VecSet, main and general cleanup

This makes both semilinear sets and linear sets use ```VecSet``` instead of ```std::set``` and improves performance by about 10-20%, so nothing spectacular but still useful.  It should also reduce the memory usage, but I haven't measured it.

Apart from that I've done some work on CLI interface -- now if you call:
- ```newton --slset``` then there will be no simplification performed
- ```newton --slset --vec-simpl``` will do only simplification of vectors (generators)
- ```newton --slset --lin-simpl``` will do both simplifications

I've renamed ```--pseudolin``` to ```--mlset```, which also respects the ```--vec-simpl``` (and will not simplify by default).

Finally, I've removed some of the code that is not needed anymore.

Everything builds on clang-3.2 and gcc-4.8.