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
added tests for testsigs for type search
restructured type classes
added tests for structure
all new tests pass, need to fix regressions
reorganized and made sure to use c_type_sig
flake8!!!