[docs] add MathOptInterface.jl to the list of packages

[odow]

Hey!

I started using this in https://github.com/jump-dev/MathOptInterface.jl

Some may find our workflow interesting.

There are a lot of tests in MOI, and it is almost entirely bottlenecked by compilation time. (I should probably experiment with Base.Experimental.@optlevel.)

We shard the tests into directories in /test, and then use ParallelTestRunner to parallelise over the files in each directory.

Each file is a module that automatically detects and runs all of the functions named test_.

I find this works much better than @testset, where I kept leaking stuff into setup and global scope and it was hard to maintain.

Now adding a test is: choose a file, add a function.

You can improve parallelisation by splitting tests into a new file

The biggest downside is that it's easy to add two functions with the same name that overwrite each other. So there's a test to avoid that:
https://github.com/jump-dev/MathOptInterface.jl/blob/ea3cf8ca0060d776bb351fe4f7e1698d308f105c/test/General/test_errors.jl#L430-L453

[giordano]

Thanks!

[vchuravy]

What is the reason for using PTR only on 64bit?

https://github.com/jump-dev/MathOptInterface.jl/blob/c5744855c655f1679acb88f1219feaf36887b214/test/runtests.jl#L49-L51