Starting tag work.

- Translation dict, contexts, parse_* and handle_* hooks in tokenizer.
Improve padding support for Tags; more code for tags in tokenizer.
Tags should fully work now in tokenizer and builder.

Still need to do attributes.
Keep .type and .tag synchronized in Tags when using their setters.
Should correctly handle closing tags with strange spacing.
Split off tag definitions into a new file.
Move repeated context checks into one block in Tokenizer._parse().
Really basic, messy, and fragile tag attribute support.
More attribute stuff.
Seems to be working for quoted attributes now.
Fix attribute behavior under certain strange circumstances.
Fix a bug in rendering Tags; attrs->attributes; update documentation.
Fix some usage of attrs; shorten a context, fix some behavior I broke.
Implement padding support for Tags completely; open_padding->padding.
_get_tag_type_from_stack() makes more sense now
Docstrings for new tokenizer methods.
Applying latest commit from develop
Merge branch 'develop' into feature/html_tags

Conflicts:
	mwparserfromhell/parser/contexts.py
	mwparserfromhell/parser/tokenizer.py
Fix handling of self-closing tags (closes #31)
Implement assertTagNodeEqual(), start test_tag(), add to tags.mwtest.