new concept of exporter with visitor pattern

-> not tested
MSMLWarning inherits UserWarning
New Version of Visitor Exporter Framework

* now with dispatching
* bug fix
* api corrected
Delete color-example.xml.py

This file was created by mistake.
Mark old exporters as deprecated.

* begin with hiflow exporter
Merge branch 'master' of https://github.com/CognitionGuidedSurgery/msml

* 'master' of https://github.com/CognitionGuidedSurgery/msml:
  Delete color-example.xml.py
current msml.xsd documentation
implement #18 partially (parameter missing)
add some viewer from the vtk python examples
vtk api has changed between 6 and 5.

Version 6.0.x is current default in fedora.
fix #25

xml.xsd is missing
move msml.xsd to msml package so it can be found
add check command for validating msm.xml only
relaxed xsd validation, bug in lxml
more "event" in visitor (for workflow, variables,...)
fixed types for simulation step
a factory for better python support

* see test_factory.py
* added msml writer from msml-gui
* bug fixes in attribute parsing
add travis.yml
Update .travis.yml
Update .travis.yml