added subsys prototype to Connection

Quick hack to allow for invoking arbitrary subsystems.
fixed tab spacing
Added example for c.subsys
Connection: verify signatures
Connection: fix DSA signature verification
Connection: only adjust DSA signature if needed
Connection: style changes, add more debug output
bump version
Parser: add more debug output
Connection: add more debug output
Parser: add more information to debug output
remove unnecessary comment
Channel: remove unnecessary error string prefixes
Connection: emit server debug messages if a debug function is set
Added step callback for SFTP.fast(Get|Put)
Update TODO
Incorporated feedback from maintainer
readme: add comment about pty use cases
Merge pull request #84 from timoxley/patch-1

Update TODO
Merge pull request #83 from ben-bradley/master

Allow invocation of arbitrary subsystems