Add Clifford+T compiler

[aijony]

For usage see src/discrete/README.md

Implements the following papers:

• Approximation of RZ as unitaries over Z[i,1/sqrt(2)] (arXiv:1212.6253v2)
• Decomposes unitaries representable by Clifford+T (arXiv:1206.5236)
• Outputs as Matsumoto Amano Normal Form (arXiv:1312.6584)

Pending on:

• https://github.com/coalton-lang/coalton/pull/533
• (Optional) https://github.com/coalton-lang/coalton/issues/534
• (Optional) https://github.com/quil-lang/quilc/pull/820

[ecpeterson]

Just wanted to drop by to say that this PR is extremely cool for a whole spread of reasons. Really excellent work.