Fix documentation for Dilithium `crypto_sign_open`

Only absorb root part of pk in haraka message hashing.

Add Rainbow

Falcon implementations (integer-only code, constant-time).

It mentioned `sk` instead of `pk` as specified in the arguments.

Closes #205.

Make a static global in Frodo const

Document what exactly hash_state.h defines

Eliminate the global state

* Names passed around (mostly constant) value more clearly
* Put ``const`` where applicable (almost everywhere)
* Renamed ``primitive.h``
* Fixed some nits

This was causing compilation failures with clang, that there were 
duplicate const keywords once the macro was expanded in hash.h

This PR sacrifices passing some extra arguments to get rid of the global
state.

* Haraka needs state in all hash calls, this results in changes to the
  hash functions specified in `hash.h`.  The extra pointers passed would
  not be necessary for SHA256 or SHAKE256.
* SHAKE256 did not have global state, but uniformity in the implementations
  requires us to pass  around the new state context anyway. Otherwise,
  @joostrijneveld's SPHINCS+ generator doesn't really work anymore).

We introduce a new header file called `primitive.h` which defines the
required state type for the generic functions. I did not go into
replacing _all_ occurrences of state variables by the new `hash_state`
macro.

Try to more reliably run the Travis PR path

Change sha3_512_inc_finalize output length to 64

Add Saber

Add release function for AES key schedule

[skip ci]