Set up an arithmetic language to play with

[bechang]

@cuplv/cuanto Team, I set up a tiny arithmetic language for us to play with. As we've discussed, the intent is that we have small languages where we own all of the infrastructure.

I want to start right from the beginning with good software engineering practices, so I spent additional time trying to document and write things in a stylistically clean way, particularly with the parser. So look in particular at the ParserSpec.scala scalatest file where I show particular examples of using scalatest: first as test-driven development unit tests and then using a bit of scalacheck (mostly tables but a built-in generator for floating point numbers).

For this first pull request, I would like everyone to review and offer comments before we accept the pull request.

Please also read the CONTRIBUTING doc for the process (which we will add to).

[coveralls]

Coverage increased (+64.7%) to 64.706% when pulling 180d7049212dec8c1473f48a196d178002c8c090 on jsy-ast into 7a509765763ece2d883f2b042eeacdfb9f4052c4 on develop.

[coveralls]

Coverage increased (+65.7%) to 65.672% when pulling e485a322f6fd982861572ca324cda9bb9342dacd on jsy-ast into 7a509765763ece2d883f2b042eeacdfb9f4052c4 on develop.

[octalsrc]

10/10