remove parser from modules.py
sys_path stuff has its own module, now.
move source_to_unicode to common
move NoErrorTokenizer to the parser, where it more or less belongs.
move NoErrorTokenizer to the tokenizer module, where it more or less belongs.
rename parser.tokenizer -> parser.tokenize
move load_module to imports
refactor ModuleWithCursor to UserContext
more UserContext improvements
moved modules.py -> parser/user_context.py