This replace the current linter with the newmoonpick linter. The new linter works against the parse tree instead of piggybacking on the compile process. Similarly to the old linter it detects global accesses and declared but unused variables. When it comes to unused variables it handles a lot more constructs, detecting unused variables resulting from destructuring statements, imports, etc. It also detects unused variables resulting from unused parameter declarations as well loop variable declarations. Another form of detection lacking altogether in the current linter is shadowing declarations, where a variable declaration of some sort shadows an existing declaration in an outer scope.

This PR removes the currentcmd.lint module, replacing it with a newlint module. It also adds alint_config.moon and updates the current code to be lint clean for the new linter (two separate commits).

Things to consider / be aware of are:

• What defaults should be used? Currently unused parameter detection is disabled by default, while unused loop variables and shadowing detections are enabled by default.
• The oldcmd.lint module is removed. This was never advertised as a public API (AFAIK), but nonetheless it might have been used by other downstream projects.
• The new API isn't documented - perhaps it should be to allow for easier integration for anyone who wishes to use it programmatically.