Add string->symbol function
Remove unneeded instructions for if
Add symbol->string and symbol=? functions
Allow comparing more than 2 strings with string=?
Refactor a bit
Actually our parser is better now!
No need for the index any more
Oops. Don't need that any more.
Remove halt option from compile method

This was only used by one caller and can just as easily be added by that caller.
Get rid of unneeded keep_last option

`keep_last: true` was only being used by specs, and `(exit)`
already accomplishes the same effect, leaving the stack intact for
Show example code that actually works
Fix error when it's on line 1
Set env PRINT_TIMINGS to show timing debug info
Show better message on syntax error
Update readme
Switch back to rust-peg and speed it up!

I was doing some stupid work repeatedly every time atom() was called.
Computing that work ahead-of-time puts rust-peg back on par with pest,
and I like rust-peg much better!
Use pest instead of rust-peg

The code is ugly, needs refactoring, but it works! And it's faster!

BUT, while optimizing this code, I realized I was doing something really
slow with find the line and column indices for each atom. That was
probably a big part of the slowness with my rust-peg implementation. So
I'd like to go back to the rust-peg implementation and see if I can make
some optimizations to get the speed closer to my implementation using pest.
Build with correct ruby
String slice is fine here
Improve how the library is found