bb.exceptions: add code to create pickleable traceback entries

bb.exceptions: add code to create pickleable traceback entries

This lets you get as much useful information as possible from traceback
entries while staying pickleable.

In addition, it has improved traceback formatting.  It shows the values of the
arguments for the functions, lines of context from the file for the code, and
has an optional formatter to do things like syntax highlighting for the code
lines.

Signed-off-by: Chris Larson <chris_larson@mentor.com>