Dxfwrite

* BUGFIX: same layer for polyline and vertex entities (Ken Healy)
* PEP8 refactorings
* Moved to GitHub.com: https://github.com/mozman/dxfwrite.git

* License changed to MIT License
* tested on Win7 with: CPython2.7, CPython3.2, CPython3.3 beta, pypy-1.9

* rewrite of DXF-String building process
* refactored MText class
* changed Viewport table entry to VPort and DXFEngine.viewport to
DXFEngine.vport. This was necessary to implement the VIEWPORT (Entity)
* added VIEWPORT (Entity) to create viewports in paper space
* view docs also on http://dxfwrite.readthedocs.org
* added some docs
* changed clothoid mirror parameters
* added methods to class `Layer`: on(), off(), freeze(), thaw(), lock(), unlock()
* tested on Win7 32 Bit with CPython-2.7, CPython-3.2 and pypy-1.7,
IronPython 2.7 failed tests - unicode issues
* tested on Ubuntu 11.10 64 Bit with CPython-2.7, CPython-3.2 and pypy-1.7

* raw unicode encoding by Toni Ruža - use any unicode character for text and table-entries.

* added easy usage of modelspace/paperspace, see examples/paperspace.py
* BUGFIX: removed dict-comprehension in module htmlcolors.py for
backward-compatibility to Python 2.5 and 2.6, works with pypy 1.4.1

* changed: set DXF Header variables now looks like dwg.header['$VAR'] = value,
see http://packages.python.org/dxfwrite/headervars.html
* splitted makedxfexamples.py into several files and moved them into the
subdir 'examples'
* curves.Ellpise: radiusx -> rx; radiusy -> ry
* moved documentation to: http://packages.python.org/dxfwrite,
and using Sphinx (http://sphinx.pocoo.org)
* tested with Python 3.2 - OK
* further compatibility-tests only for CPython 2.7 & CPython 3.2+
* added Drawing.add_xref(filename), for usage see examples/xref.py
* adding relative attributes by Insert.add() consider the xy-scaling
* added `Howtos` section to documentation