add some racket support

[odanoburu]

• submitting input to racket REPL now works out-of-the-box
• go-to definition works

added some definitions to racket-mode too, see greghendershott/racket-mode#374

[coveralls]

Coverage decreased (-0.01%) to 62.769% when pulling d0ff772 on odanoburu:racket into 27282ca on abo-abo:master.

[abo-abo]

Thanks. Merged with minor changes, please review.

I also added some limited support for eval. It doesn't display any stdout, only the return value. But better than nothing.

I wonder, why not just use Geiser? Is racket-repl better?

[odanoburu]

I also added some limited support for eval.

thanks! I saw some people wanted this feature in racket-mode's issues.

I wonder, why not just use Geiser?

tbh, I haven't even tried it. because racket is not scheme anymore i thought things might break :P