Start writing a more complete documentation for the library.

Update the README with a link to the current draft of the documentation.
This is temporary, at a later stage the documentation will be directly
included in this repository.

Closes #1

Do not assume that the `colors` parameter of the scatterplot
function is a string of one-letter color codes.

Add a list of available modules in the package.

Right-trim white lines.

Add a new module providing a helper function to draw barplots.

Prevent the pvalue symbol from overlapping with the underlying hline.

Compute a min_sep value depending on the span of the values to
distribute.

Reduce slightly code redundancy by using a helper function to select
the dataseries to plot for each subtrack.

The scatterplot function can automatically perform a statistical test
between two subtracks.

Add some more classifiers to the setup script and all the expected
distribution files, including a very basic README.

Add basic docstring to public functions. The scatterplot function
will probably need more documentation if it is to be helpful to
anyone but me...

This is Incenp.org's PyPlot, a Python helper library for plotting
tasks.