Rename entryPoints to injects.

This is closer to what we actually do. It's a type that can be
injected. There's a slight bit of ambiguity because we use 'inject'
to describe types that are included implicitly. I don't anticipate
this to be a problem in practice.
Merge pull request #221 from square/jwilson/rename_entry_point

Rename entryPoints to injects.