[noise] New draft: "Patterns" terminology

[Trevor Perrin]

Some people weren't finding it clear that Noise could be used for
other protocols besides the Box?? and Handshake?? constructs.  I've
tried to clarify that.

I also renamed these constructs as "patterns" which are combined with
a ciphersuite and other processing logic to create a "protocol", since
the patterns are more abstract than a full protocol:

https://github.com/trevp/noise/blob/master/noise.md

"""
2.4. Protocols and patterns

A sequence of descriptors for pre-messages and messages is a Noise
pattern. A simple pattern might describe a single box message that
encrypts one plaintext from Alice to Bob. A more complex pattern might
describe an interactive handshake whereby Alice and Bob mutually
authenticate and arrive at a shared session key with forward secrecy.

A Noise-based protocol combines a pattern and a ciphersuite. It may
also specify how to initialize Noise session(s), or specify other
operations to perform on the sessions (see Section 5.3). Finally it
may specify application-specific processing rules.

Some example Noise patterns are defined in Section 7.
"""

Trevor