added self.ns namespace parameter to anaphoricity importer
added namespace parameter to conano importer
added name/namespace parameters to rst importer
fixed anaphoricity name parameter setting
added self.root to rst importer
closes #20: added namespace parameter to tiger importer
flake8: merging.py
add get_tokens() to DiscourseDocumentGraph
get_tokens() now returns (token node ID, token string) tuples
get_tokens takes token node attribute as parameter
fixes #21: merging works w/out tiger_tokenlist/rst_tokenlist
closes #23: RST files are tokenized during import
cleanup: removed old TODO
fixed namespace handling in TigerXML importer
TigerXML importer: added explicit node labels for dot export
RST importer: added explicit node/edge labels for dot export
conano importer: don't add precedence relations by default
rst importer: updated docstring
added generic merging method to DiscourseDocumentgraph base class
fixes #19: merging.py now uses generic merging method