Add support for constraint programming about flips

[matthewcrews]

@Shmew I've been reading up on this and it appears to be a different enough domain that I think I would rather create a different library for that domain. My goal with this library was to create something simple specifically for LP/MIP.

It's sounds like an interesting problem though! I am going to need to do some more reading up and look at some real world problems to get my head around it.

I am also actively trying to learn more about Category and Type Theory in order to come up with better abstractions. There are some features coming in F# 5.0 which will make all of this easier.

This library was a great learning experience though and lays a foundation for doing this work. I have learned a ton from this experience and making something equivalent for CP-SAT Solver will likely be much faster.

[matthewcrews]

@Shmew Could you provide me some example problems/formulations with solutions that I can use for a test bed? I am wanting to understand the problem space to make sure that we get the "ergonomics" of using the library correct.

I am thinking that this will likely involve some new types to ensure that people do not try to use an incorrect type of model/solver combination.

Also, if you have any recommended literature/textbooks on the subject, I would love to hear about it. I have not worked in this domain much so I would like to get up to speed. Thanks for the help!

[Shmew]

Here's an example (that's probably poorly done) gist. This was to find the optimal schedule given the constraints defined in the json file for the job shop problem. I don't have much in terms of recommendations, I pretty much fumbled through this until I got something that I believed to be working.

Honestly it was a pain to get this far, as their documentation in many parts was python only, and pretty sparse. I had to trawl through the repo issues/google group/source code to figure out how to do it all, especially in a non-imperative style.

[NatElkins]

Just want to chime in, I also have this use case. I'm probably going to take a crack at using the Google OR library directly for a problem that is very similar to this one: https://developers.google.com/optimization/scheduling/employee_scheduling

There's a good .NET example here: https://github.com/google/or-tools/blob/master/examples/dotnet/ShiftSchedulingSat.cs

[matthewcrews]

I will be addressing this request with the Coffy Library. I will be adding this discussion to that library.

COFFY: Constraint Optimization For Fsharp Yay