Merge pull request
#1855 from minrk/moremagics
%%script and %%file magics
* `%%file` writes to a file (-f to force overwrite)
* `%%script` runs a cell with a particular script
The ScriptMagics also defines a few common magics that wrap `%%script` with common interpreters, such as `%%bash` by default, and this list, as well as the full path for each, is configurable.
For fun, the `%%script` magic is also presented as `%%!`.
