Update to jsch 0.1.50
Factor out keypair generation

Simplifies add-identity by factoring out the keypair creation.
Allow generate-keypair to write key files
Updated version, release notes and readme for 0.5.6
Merge branch 'release/0.5.6'
Merge tag '0.5.6' into develop

clj-ssh-0.5.6
Updated version for next release cycle