Merge pull request #7 from tclose/adding_dimension_attributes

Added dimensions to state variable objects and all xml writer methods
mend

added reader support for piecewise mathinline
Merge branch 'modular' of https://github.com/apdavison/nineml into
adding_mathinline_piecewise

Conflicts:
	lib9ml/python/nineml/abstraction_layer/dynamics/component/expressions.py
	lib9ml/python/nineml/abstraction_layer/dynamics/readers/xml_reader.py
Merge branch 'adding_mathinline_piecewise'