Python 3 compatibility.

--HG--
branch : 1.8
Move fixtures to central conftest file.

--HG--
branch : 1.8
Basic py.test configuration

--HG--
branch : 1.8
Format warning about charts.

--HG--
branch : 1.8
Add development notes to TOC

--HG--
branch : 1.8
Test configuration handled solely by tox to avoid race condition problems with dependencies.

--HG--
branch : 1.8
Sample file for adding images.

--HG--
branch : 1.8
Reverted image count.

--HG--
branch : 1.8
Convert test expressions to assert statements (nose to pytest)

--HG--
branch : 1.8
Some additional basic fixtures

--HG--
branch : 1.8
Convert setup methods to fixtures,

--HG--
branch : 1.8
Removed image tests as replaced by ones in test_drawing.py

--HG--
branch : 1.8
Moved chart writer tests into separate movule and class fixtures to conftest

--HG--
branch : 1.8