Rename interpreters and type checkers, replace `-` with `_`, to match the book

[jsiek]

I've already done it for interp_Lint and interp_Lvar.

[Temperz87]

Looking at the book it seems like some interpreters/typecheckers (e.g. L-any) are still labeled using dashes and not underscores, should I leave them untouched?

[jsiek]

Let's change those as well, and update the book.

[Temperz87]

Why is it called interp-poly and not interp-Lpoly?

[jsiek]

I don't remember.