Flesh 0.1.0 - harder better faster STARTTLSer

General changes
  - new TCP Portal
  - STARTTLS is supported

Portal interface changes
  - new opaque socket type, containing the inner socket
  - t is a record, with stream push and socket
  - header (formerly stanza_open) transmits the opening stanza instead of returning one
  - push None automatically closes the stream
  - new starttls method
  - new _encrypted function, testing if a socket is encrypted

Flesh changes
  - Full authentication flow supported, from opening the TCP socket to <success/>
  - Stream supports parsing feature list and negotiates mandatory features
  - remove the cumbersome features struct and favor a simple features variant type
  - new Starttls module
  - Wire module for lower-level operations