Numerical optimization section of the reference manual needs reorganization

Dima:

Numerical Optimization section should be split into parts. It's a weird mix of discrete optimization (Knapsack)--- out of place there, as it's not "numerical", but discrete, with numerical root finding, least squares approximation, and optimization of functions of one variable, and linear (LP), integer linear (ILP)---again, a discrete problem--- and semidefinite programming (SDP).
By right, LP and SDP should be put into its own "Convex optimization", Knapsack and ILP into "Discrete optimization", and univariate things into "Calculus/numerical methods". I also think that the code for the latter and for Knapsack should be split into separate files - currently they are all dumped in numerical/optimize.py, which also contains a little function to demonstrate the direct use of cvxopt LP solver---the latter should also be somewhere else.
Note that ILP and LP are solved by the same frontend, specifying appropriate parameters, so I don't quite know how to structure the corresponding documentation. (Probably one would have to link to .rst files that further point at the concrete code documentation?)

Johan:

Numberical Optimization is semantically linked to SAT Solvers. Perhaps they should simply have their own headline called Solvers or something.

CC: @dimpase @mkoeppe @mforets

Component: documentation

sagemath / sage