Make snf-image-creator be the dialog-based program and snf-mkimage be
the command line one.

 * Prefix all private methods with _
 * Write missing docstrings
 * Move all public methods above the private ones
 * Add module docstrings where missing
 * Define source code encodings on all modules

Support both versions (1.2.x and 2.x) of python-sendfile. In
v1.2.x (py-sendfile) the returning value of the sendfile function is a
tuple, where in v2.x (pysendfile) it's a simple integer.

This reverts commit 883e57b0.
Drop the greenlet support.

Needed by new kamaki, otherwise it throughs an exception at the end.

The former is older but there are packages for it in distros like
Ubuntu.

PBS has now bocome sh.

Add progress >= 1.0.2 as install_dependency, since this is the version
that fixed the empty progress bar problem.

Also add a basic readme file.

Create a new dialog_menu module to host all the "expert mode" code.
Check the code with a new version of pep8

This dir will host help files used by snf-image-create-dialog

snf-image-creator-dialog is a dialog based version of snf-image-creator
Nothing works yet

The package is buggy and we can use pbs to do the same thing.