add __repr__ on NotAvailable, NotLoaded and _NO_DEFAULT constants to be more readable on doc
add documentation on object constants
[vimeo] catch HttpNotFound errors
Configure isort and flake8
pastebin: Handle limit exceeded warning

And skip if found in tests
pastebin: Fix crash with Base() and filter chaining

Revert to old style filters for now, investigate later.
release.sh: Use a better LANG
Centralize encoding guesses, default to UTF-8

This might not be enough for print() and could need a locale.setlocale()
even though it is generally discouraged.

closes #1352
pastoob: Add an option to set a custom file encoding
Use class attributes as much as possible for application output

refs #803