Add a non-interactive mode

[georgebrock]

gitsh should accept commands via STDIN or the path to a script as an argument. Scripting support will require additional features, like variables.

[mike-burns]

Should be usable as a sh-bang.

[georgebrock]

Using gitsh as a sh-bang line will be tricky, since gitsh itself has a sh-bang line:
http://stackoverflow.com/questions/9988125/shebang-pointing-to-script-also-having-shebang-is-effectively-ignored

[mike-burns]

Writing a tiny C wrapper would also make #41 possible.

[mike-burns]

See also: http://www.in-ulm.de/~mascheck/various/shebang/ especially "nterpreter itself as #! script".

[georgebrock]

Work in progress on the gb-non-interactive branch: https://github.com/thoughtbot/gitsh/compare/gb-non-interactive

[georgebrock]

#171 adds support for passing a path to a script file as an argument. We still need to accept scripts piped to standard input, though.

[georgebrock]

#175 adds support for piping commands to the standard input, so we're done!