across string2/containers. Modified the type stuff to output better type
names and use (a Dict) and (a List) instead of (Dict) and (List). (Text)
now also has a proper constructor. (assume) now also handles a bunch of
different assumptions with smart error messages.
better error reporting, e.g. for (fail) (no arguments). Overall better
error reporting now. Also added shorthand ("Action" tree with ...) for
(SyntaxTree {.type = "Action", .1 = ...}).
