Add docs to the writeandexecute magic
Magic to mark a cell as inactive

The cell will simple *not* be executed.

In [1]: %load_ext ipython_extensions.inactive
'inactive' magic loaded.

In [2]: %%inactive
   ...: print "nothing"
   ...:
Cell inactive: not executed!
Merge pull request #13 from JanSchulz/inactive_magic

Inactive magic and doc updates to writeandexecute magic