merlin 0.4.0

Composable proof transcripts for public-coin arguments of knowledge
Documentation
# 0.3

* Forces labels to be `&'static`
* Merlin-specific domain separator
* Use a pointer cast instead of a transmute
* Clarify example documentation

# 0.2

* Adds a TranscriptRng for use by the prover.

# 0.1

* Initial prototype version.