[equations] Generate AMR output for equation-based input

[myedibleenso]

In coordination with @Free-Quarks , add AMR service for output to equations-rest example.

Tasks

Beta Give feedback

1. Relax /mml/amr constraints to handle pMML output from /image/mml skema#289
   MORAE +1
   
2. Add notebook

[myedibleenso]

@Free-Quarks , are there expectations we need to keep in mind about the pMML that you take as input?

[Free-Quarks]

For the eqn2amr endpoints, not really. Just a vector of mathml strings, each string being one equation of the system of equations.

We don't have complete coverage over everything that can popup in pMML, but when it comes to the standard first order linear differential equations of our domain, it should be very good coverage.

[myedibleenso]

initial version completed during the hackathon.