Improved and rewrote rendering.
Improved and rewrote rendering.

- Using PrettyPrinter subclass to handle exceptions in values.
- Replaced the global pformat() hack with regular _format_xxx()
  functions. Also fixes ',' sign at the end of values.
- simplier appearance of BlockNode
- better appearance of exceptions

edoburu/django-debugtools,edoburu/django-debugtools,edoburu/django-debugtools