Add support for all remaining simple escape sequences

[jianlingzhong]

This closes #97.

[CLAassistant]

All committers have signed the CLA.

[jeaye]

So, there's some missing work here. Check out the steps in the ticket for details: https://github.com/jank-lang/jank/issues/97

We've done the first and third, as part of this PR, but the second and fourth are needed in order for this to fully work. Right now, we will lex these escape sequences, but they won't be parsed properly. To see what I mean, try this:

$ jank repl
> "\v"

[jianlingzhong]

@jeaye updated. could you take another look?

[jeaye]

Looks great!