[MOF] Begin formal JSON schema

[odow]

Still todo

• is there a way to validate variable names used in functions are defined in variables? Don't think so
• nonlinear functions
• variable and constraint attributes other than Name
• rebase on Refactor some MOF fields #49 once merged

Closes #46

[mlubin]

This is great. It's even easier to read than I expected.

[odow]

Yes, it's very easy to read. I wonder if we should include the math descriptions for all functions and sets in the schema so that it is virtually self-documenting.

[Wikunia]

Based on

{
     "coefficient": 2,
     "variable_1": "x",
     "variable_2": "y"
 }

it should be min{x^2 + 2 * x * y + y^2}, right?

[odow]

Oops. You're right that there is a mistake but that is the wrong one. I doubled the wrong value.

This is an annoying point that has come up a few times (e.g., JuliaOpt/LinQuadOptInterface.jl#22).

MOI defines the ScalarQuadraticFunction as 0.5 x' Q x.

[odow]

Merging since I think we're fairly happy with this. We can address any other points in future PR's.