Rename Scp to ScpBuf, add Scp for files.

Updated cmd_run.go to use ScpBuf.
Working sendfile.
rename sendfile to push
finish renaming sendfile to push
Update comments.
implement ScpPull, safer args to scp, cleanups
Stub out gdsh pull - working, but needs arg parsing

This is almost done and currently working on my local setup.
Explain newly implemented commands.