refactor: handful of linter appeasing code changes

[launeh]

Really only intended to add @types/mocha to the dev dependencies and make a handful of linter appeasing changes:

1. add 'const' to ohm where missing
2. explicit .toString() on Buffer when initializing grammar.

Auto-formatter made the other changes (whitespace and semicolon insertion)

[dkrasner]

yeah we need better linting here throughout the co debase

[launeh]

added basic linting: #137