v0.2.0

This release breaks several APIs so please review your code.

The first break is that UBootEnv.encode/2 returns iodata now. In general, the
return value would end up being passed places that supported iodata, but it had
previously been spec'd as returning a binary.

The second break is that UBootEnv.decode/1 now does the reverse of
UBootEnv.encode/2. It previously was a convenience method, but it was public.
It is not expected that many people used the previous function.

• Bug fixes
  • Reduce the amount of garbage generated when encoding and decoding. A manual
    call to :erlang.garbage_collect/1 can free the garbage, but it stays
    around long enough to make any process calling this library to show up with
    megabytes more heap used.