Tell a better generative story

[joshrule]

Right now, we can use macros to create type variables without reference to a context, and we might also be able to do this with the parser, too. Trying to then incorporate these types into a system which uses a type context can lead to conflicts that either leads to failed type inferences (false negatives) or spurious type inferences (false positives). Telling a better generative story in which type variables are always created by a context might solve this issue.