add bool literals in surface language, and other minor stuff

Pretty: instead of ad-hoc `instance Render [Foo]` per-`Foo` (especially annoying when there is also `With metadata Foo` and so on), add a `listSeparator` method each `Foo` can use to customize how lists of it are rendered, and define a single `instance Render a => Render [a]` based on that

Allow the LHS of a call to be an expression (instead of just a name). That was /almost/ easy...

{Name,Type}: keep a stack of metadata for better robustness, track it at finer-grain in function signatures, other minor refactoring

support writing function and unit types in the source language, and do some pretty significant surgery on `module Type`...

add a separate `Type` node type to the AST so we also get proper location info for name lookup errors in signatures

Type: add location/metadata to errors in the same way as `Name`

Name: report errors with metadata (i.e., locations); also rename the type variable for annotations to `metadata` everywhere in the project

AST: fill in the `exitTarget`s again

make `resolvePrecedences` work again, fix a couple of infinite loops, and assorted minor cleanups

add annotations (source locations) to AST and parser and make everything compile. this was way too much work... TODO: `AST.resolvePrecedences` is still stubbed out

for posterity -- I tried to make the AST generic over an arbitrary Functor `f`, and it's kinda nice and mostly works, except `deriving` can't handle it (typical), and I don't /think/ it actually makes sense -- maybe you could instantiate it to `Either TypeError` for more fault-tolerance, or something? but for now let's keep things simple and specialize it to just annotations

`RecursiveDo` out of `default-extensions`

Token: reimplement using `lexer-applicative`. it... just works?

IR: use `whenM`, `ifM`, `elseM`