New package for linear optimization problems

[SamoylovMD]

We could add new package for linear optimization with linear constraints (for more information see http://en.wikipedia.org/wiki/Linear_programming) - I think it should be added in 0.6.0 or one of future releases.

[vkostyukov]

I've put a 0.6.0 label. We will revise it later.

I think we should focus on the functionality we have right now and keep making it faster and faster.