Implement box-swap!
Merge pull request #19 from qerub/master

Add if-not and when-not to feature list
Return immutable strings from str.
Add egal.rkt.
Merge pull request #20 from technomancy/immutable-string

Return immutable strings from str.
Merge pull request #21 from technomancy/egal

Add egal.rkt.
Update contract to add immutable?
Change unit tests to exercise contracts.
More-reliable test of {1 2 3} syntax error.
Use racket/base and require what's needed
`(sequence? pair?)` is #f

Instead, check for `pair?` and use `equal?` (don't want `eq?`).
Add unit tests for `egal`
Merge pull request #22 from greghendershott/egal-test

Add tests for `egal` and fix issue with pairs
Update copyright year.
Add technomancy to THANKS
Update README:

- Document `egal?`.

- Note that `str` returns an immutable string (as of commit
  949042c).
Bump to v0.2
Add caveat about `egal?` and `struct`s
Make `egal?` handle `struct`s. Closes #23.
Merge branch 'qerub-box-swap'

* qerub-box-swap:
  Implement box-swap!