Numerous fixes
Unicode updates:
- Default output encoding is the same as the input unless specified by new CLI output_encoding
- References can have different input encoding assigned to them
YAML changes:
- Default setting file is now in YAML
- Default setting file renamed to pymdown.cfg
- Fix for loading YAML config.  Would fail on parsing YAML
General Fixes:
- If no template is provided, still output markdown
- Simplify code in some places
- Comment better in some places
Additions:
- allow setting of tab_length, lazy_ol, and smart_emphasis
- Output "Table of Contents" title for toc extension by default in default settings