Added exec subsystem
Added docs for exec subsystem, and minor change to getError, it now calls getResource
Minor grammer fix to readme
Minor method call fix in readme Exec example
Refactor to only call ssh2_exec on run
Add getExec to get the exec subsystem from session
Update readme to reflect api changes
Minor runtime exception no longer thrown
Throw exception on error from command
Merge pull request #6 from camspiers/subsystem-exec

Subsystem exec