Merge pull request #51 from rethab/master

gitignore cabal sandbox and some spellings in Backend.hs
use byteable to get a -> Bytestring function.
remove old code commented
Export the partial capability and wrap it in a easier layer.

now runGet has the ability to return partial result and unparsed bytes.
put the type of the handshake for the parsing of handshake message.
Allow handshake records to be split across records.

* Store continuations in record state
* parse handshake records one by one.
Fix supported protocol versions in simple client being too strict

allow protocol versions downgrade unless the no-downgrade flag is set.
add a Changelog.
add CHANGELOG file
bump version to 1.2.3
bump version to 0.3.1