Reorder imports
Create LanguageName type synonym

Rationale for name choice: in
https://github.com/Blaisorblade/pts/commit/3f5d125ba5e566e10000f08aa7e28f62917ea87b#commitcomment-7362848
Tillmann wrote:

> Can we call this LanguageName, as part of a slow move towards using
"language" more and "PTS" less. Reason: In the future, I consider
non-PTS language options like "records available" or "type inference
enabled".
Split PTS instance lookup out of PTS.Options

We're going to need this code to implement "language foo;".
Merge pull request #122 from Blaisorblade/topic/language-prepare

Prepare for language statement