(Bug 5238) Return an empty hashref instead of undef

This makes it so callers don't have to care whether the POST was valid
or not, when looking up whether something might be in $r->post_args
(Bug 5241) Fix whitespace and long lines; update revision date.

- Rewrap excessively long lines

- Remove trailing whitespace

- Update "last revised" date to today
(Bug 5238) Return an empty Hash::MultiValue in case POST was invalid
Merge pull request #554 from afuna/bug5238-no-post_args

(Bug 5238) Return an empty hashref instead of undef
(Bug 5241) Reword TOS to omit mention of invite codes.

Invite codes are no longer required - update the terms to reflect reality.
(bug 5205) Add admin post status to ESN notifs
Merge pull request #558 from anall/feature/bug5205

(bug 5205) Add admin post status to ESN notifs
Merge pull request #555 from kareila/bug5241-tos

(Bug 5241) Reword TOS for optional invite codes.
Merge branch 'release-1.18' into develop

* release-1.18:
  (Bug 5238) Return an empty Hash::MultiValue in case POST was invalid
  (Bug 5238) Return an empty hashref instead of undef