style, pep8, and use iteritems

rm remnant print
bugfix: add missing to_python
add attr GRSpec._parts for easy reference
extract garbage collector from GRSpec.parse
cache gr1c and jtlv strings in GRSpec
replace lexical var name substitution in jtlv interface with correct flattening in GRSpec
rm redundant parsing

because to_jtlv invokes parsing if needed.
hide function finite_domain2ints in spec.form
pep8, style, use str.format, minor refactoring, more logging
rename load_file to jtlv_output_to_networkx

and load the jtlv output outside that function, because it leads to better separation of functionality.
use natsort to sort the states in FTS.__str__