updated docstrings and minor stuff
trap_spaces: updated docstrings
add_style_path: added penwidth argument
[bugfix] subgraphs2tree: false detection of non-trivial intersection fixed.
added STGs.compute_attractors with test and docstring
stg2dot: heuristic scaling based on update strategy
typos
renamed SUCCESSORS to CHANGING and finished docstrings
added PyBoolNet.version() to query its version
StateTransitionGraphs:successors: bugfix for state given as str.
