Move riemann_surface_path to top abelfunctions level.
Move doc source to separate directory.
Add initial doc source files.
Add basic structure of documentation.

Establish basic structure of the documentation and add
some simple content.
Add sphinx13 documentation theme.
Expand stubs and add logo to documentation.
Add numpydoc to documentation extensions.
Add refactored RiemannSurfacePaths and dependencies.

The refactored RiemannSurfacePaths successfully compile, but are not
tested. They depend on an AnalyticContinuator object for determining
y-values.

A stub for RiemannSurfaces is created.

setup.py and .gitignore are updated to reflect these additions.