Port build system to new plugin API. test_build passes.

Htmlifiers no longer exist; we now simply pass the iterables of refs and regions around.

Remove the assumption that file contents are encoded UTF-8. They're now Unicode, and we explicitly don't try to mark up binary files.
Fix crasher in all_plugins(). test_plugins now passes again.
removed networkx dependency
Removed networkx dependency. Closes #296
Merge branch 'remove_networkx' into es
moved enviornment function from indexer to plugin
prototype for stateful clang indexer
scaffolding for FileToIndex
failing on correct order...need to fix
incorrect order test fixed
working on needles
setting up scaffolding for FiletoIndex
added mock to requirements
scaffold for needle tests
create fixture to share between tests
consolidate tests to take advantage of common fixtures
wrote some needle tests
added group needles helper function + tests
registered all the needles
implemented standard needles
callee and caller needles