Get rid of extra fields for failures within the Action layer.
Rip out failure fields from the validation layer.
Get rid of failure fields in documentation.
Remove some no longer accurate docs.
Suggest way of including additional information in failed actions.
Merge branch 'python3-1' into no-failure-fields-14
News entry.
Merge remote-tracking branch 'refs/remotes/origin/master' into no-failure-fields-14

Conflicts:
	docs/source/usage.rst
	eliot/_action.py
	eliot/tests/test_action.py
Fix failing test.
Fix typo.
Merge pull request #36 from hybridcluster/no-failure-fields-14

No failure fields.

Fixes #14.