Writing commands:
-----------------

TODO: this is a * bit * out of date now.

Subclass from Command.

Be careful not to import INARY modules before Command is run, e.g.
do it in run() method. This is necessary to prevent an obscure
initialization error.

We used to import inary.operations in inary.cli

This prevented inary.operations from having the current global
inary.ui.ui because it's loaded before the UI is set! So, despite
what you might understand from the python FAQ 1.2.3
# how-do-i-share-global-variables-across-modules
http: // www.python.org / doc / faq / programming.html
you have to be careful about the initialization order when using
singleton modules.

Another way to solve this is to ensure that the global module is
always imported again in every function it is called(see
                                                     ui.CLI.confirm()) but this is more expensive.
