Merge pull request #1 from tclose/modular

pep8 fixes
fixed bad indentation
replaced '^' with 'pow(?,?)' so expressions can be parsed by yacc
added dimension keyword argument to ports
Merge pull request #3 from tclose/biophysics

Minor bug fixes
Merge branch 'modular' of https://github.com/apdavison/nineml into
divided_up_user_layer

Conflicts:
	lib9ml/python/nineml/abstraction_layer/dynamics/component/parse/expr_parse.py