use MTK macro processing code instead of writing custom DSL code

[isaacsas]

On a quick skim, it appears subsets of our DSL macro processing code overlap with MTK macro processing code. We should switch to MTK's code as much as possible to avoid needing to maintain our own macros (for example @equation), and to ensure feature compatibility with MTK.

edit: Perhaps this isn't possible but it would be good to really make sure we can't reuse their code (similar to how we defined @species using their code as a base).