FIX: Make legends show up in ipyton notebook

This adds a workaround for a bug in the tight layout code in
matplotlib. The next version of matplotlib has the same fix
internaly, so this workaround is not needed for  matplotlib >1.3.1
https://github.com/matplotlib/matplotlib/issues/2530

Closes: yhat/ggplot#33

stat_function added
Removed excess shebangs
Add support for Travis and Coveralls, and added requirements into setup.py.
Update README.rst to contain same content as README.md and delete the latter
Add absolute URL to README.rst so that PyPI version won't look bad
Fix absolute URLs to point to main repository instead of my fork.
Fix missing paren in tests/test_geom_histogram.py
Add miniconda.sh to repository to simplify Travis setup and prevent issues if main Continuum server goes down.
Change .travis.yml to install matplotlib 1.1.1 and pandas 0.12
Update image URLs in README.rst
Remove public/img folder since we're just using baseline_images now.
Install matplotlib 1.1.1 for 2.7, but install latest for 3.3
TST: Disable tiff saving test (travis failure)
Add Travis badge on readme
Workaround for matplotlib 1.1.1 and missing rc_context

Monkey patch the rc_context into this old version on import
Use our own image testing framework for anti-aliased text

Currently baseline images, which were generated on *ix(?)
systems fail on windows computer as windows systems produces
different baseline images which are *NOT* anti-aliased.
I traced that to a line in matplotlib, which setups the
rc context to not use anti aliasing and it seems that the
rc-context used during `ggplot.draw()` which uses
anti-aliased fonts is not used when the image is
saved in the `image_comparison` decorator.

This commit replicates the matplotlib testing framework, but
sets anti-aliased to true and also uses only pngs.

There are now two ways to test for same image:

* `@image_comparison` decorator (similar as in matplotlib)
* `assert_same_ggplot(gg, "name")`

The latter needs some setup to to locate the baseline images:

```
from . import get_assert_same_ggplot, cleanup
assert_same_ggplot = get_assert_same_ggplot(__file__)
```

This fix is also needed when we want to support matplotlib 1.1.1,
as this old version does not support using the `image_comparison`
decorator outside of matplotlib.
FIX: old usage of facet_grid in old manual tests
TST/FIX: fix test_scale_log and port it to the new testing framework
TST: don't use the manual test, only the real unittests
FIX: ggsave needs to close a drawn plot

Up to now, ggsave(ggplot_object) would draw the plot and this would
then show up in ipthon notebook. So

```python
gg = ggplot(...)
print(gg)
ggsave(gg)
```

would show the plot twice.

closes: yhat/ggplot#140