hook,processor: Adds wait_time() scripting callback hook.

Closes chfoo/wpull#114.
Adds unit tests for wait_time() hook.
Merge branch 'issue/114-wait_time_hook' into develop
Bumps version & changelog to 0.32.1
Merge branch 'release/v0.32.1' into develop
document.py: Catches any lxml.etree errors parsing doctype.

Closes chfoo/wpull#118.
scraper: Handles catching of UnicodeError/LxmlError. Allows partial scrapes.

processor: Don't catch UnicodeError.