Fix #158: only check result after async transition
Rename PyplotCurveViewer to PyplotViewer

Fixes #143
Allow x to be None by PyplotViewer

This resembles more what pyplot does and might be useful.
Re-enable tuple plotting

That is necessary for PyplotViewer usage as a coroutine.
Make focusing plot ouput more lucid

Don't plot (x, y) but (iteration, y), that helps the user
to follow what is really going on.
FileCamera directory can be set on-the-fly

This is useful for tomography testing where one has
the data in different directories.
Revert "FileCamera directory can be set on-the-fly"

This reverts commit 063499dcc595a3d4ab7bbaa04f8a4745bdef1c53.
Use Python 3.3 and fix requirements in tox
Fix #147: Split coroutine module and unify API

For the second part, the generate_sinograms was renamed and made a real
coroutine with a consumer argument.
Added absorptivity filter
Stop flake8 complaining about too long lines

Although PEP8 generally advises to use 79 characters, there is an exception
given:

> Some teams strongly prefer a longer line length. For code maintained
> exclusively or primarily by a team that can reach agreement on this issue, it
> is okay to increase the nominal line length from 80 to 100 characters
> (effectively increasing the maximum length to 99 characters), provided that
> comments and docstrings are still wrapped at 72 characters.

Hereby, the limit is lifted to 99 characters and flake8 stopped from being
complaining. If you need longer lines, consider refactoring your code by writing
functions or store intermediate results in variables.
Implement state machine transitions for Parameters