Split out rST parsing code to a new frontend
Rename StyleStore to StyleSheet and require a name on instantiation
Move some fonts to this rinohlib namespace package (PEP 420)

The rinohlib namespace package collects all optional RinohType components
such as fonts, style sheets and document templates.

There are some problems with namespace packages though:

- It doesn't seem possible to discover which packages are installed that
  reside under a namespace package.
- One cannot have an __init__.py in a namespace package. This leads to the
  the following less-than-perfect import:

      from rinohlib.fonts.texgyre.pagella import typeface as pagella
Move the reStructuredText example style sheet to rinohlib
Also move the RFIC example style sheet to rinohlib
Adjust the IEEE style sheet so that it can also be used in the rST example

It works, but doesn't look good.
Fix numbering of section titles in the rST example
Allow for the creation of derived style sheets

StyleSheet now accepts an optional base (StyleSheet) argument.

- If a style is not found in a StyleSheet, it is looked up in the base.
- When matching against Selectors, the Selectors of the base StyleSheet are
  also tested.

Selectors map Styled instances to style *names*. From the name, the
corresponding Style is looked up in the top-level StyleSheet. This means
that existing styles in a base StyleSheet can be easily overridden.
Some refactoring in StyleSheet.find_style()
Introduce WarnFlowable: no rendering but do print a warning

Used to handle docutils system messages.
Adjust the IEEE style sheet to properly handle nested lists
Make DefinitionList take Flowables for the term and the definition
Map title-reference node to enable rendering of COPYING.TXT
Tidy up display of long list item paragraphs
Enable rendering of README.txt

- Map the comment node
- NestedElement.process_content() should start from a MixedStyledText to
  allow concatenation with Flowables (wich become nested flowables)
- Some style improvements
Use setuptools instead of disutils

- Python 3.3 breaks pkgutil.walk_packages
- setuptools is now the recommended packaging tool
Provide a more useful README

- information on requirements and how to run the examples
- scripts to easily run the examples
- disable setup.py until the rinohlib namespace package situation is
clear