DONE: rework type system
DONE: var decl with a type, but no value
DONE: type casting
DONE: remove optimization option
DONE: conditionals
DONE: if-then-else
DONE: chained if-then-else
DONE: optional block around a path if it's only one statement
DONE: while-then
DONE: for-then
DONE: break and continue statements
DONE: truthiness rethink
DONE: string concat with the + operator
DONE: increment & decrement operators
DONE: store compound types in variables
DONE: +=  -=  *=  /=  %= operators
DONE: && and || operators
DONE: functions are invoked by calling their names
DONE: function arguments can have specified types
DONE: function returns can have specified types
DONE: closures are explicitly supported
DONE: functions are first-class citizens
DONE: functions take a set number of parameters
DONE: functions last argument can be a rest parameter
DONE: assert needs to kill the whole script, not just functions
DONE: native functions
DONE: global functions _get, _set, _push, _pop, _length, clear available
DONE: change comma to colon in dictionary definition


TODO: slice and dot notation around the _index function
TODO: ternary operator
TODO: Nullish types
TODO: A way to check the type of a variable (typeOf keyword)
TODO: a = b = c = 1; ?
TODO: are compounds shallow or deep copies?
TODO: Address circular references?
TODO: Assertion-based test scripts
TODO: standard library
TODO: external runner library
TODO: document how it all works
TODO: third output stream, for parser/compiler/interpreter errors
TODO: better and more consistent error messages

NOPE: functions return a set number of values