Fix docstring.
Add Doxygen comments to the exception translator.
Fix high-level module Python 'viennagrid'.

* Describe arguments for point constructor in its docstring.
* Fix attribute name in 'Cell.vertices.VertexList'.
* Add property to access the facets of a cell.
* Add method to get a point object from a vertex object.
Fix CMakeLists to build the Sphinx documentation and include it in the Python distribution.
Create files to reimplement I/O and add them to CMakeLists.
Implement and wrap Netgen reader.
Implement and wrap VTK reader.
Implement and wrap OpenDX writer.
Implement and wrap VTK writer.
Delete old readers and writers.
Add docstrings to new readers and writers.
Implement high-level readers and writers.
Update Sphinx documentation.

* Update Sphinx documentation to include the new implementation of readers and writers.
* Change required ViennaGrid version from 1.0.1 to 1.1.0.
Merge branch 'io' into devel

Refactor readers and writers.
Fix distutils 'setup.py' to solve problem with 'make install'.

In a previous commit, a line from the 'setup.py' was removed. After this, 'make install' complains that there is no directory named 'viennagrid'. Adding this line again solves the issue.
Fix Python module 'viennagrid.config'.