Expand out URLs truncated from Campfire exports

URLs get trimmed when dumped into the chatroom, and it's this
version which happens to carry across when exporting the text
dump.

This attempts to fix some of them, where their full address
can be reasonably guessed. For the most part.
Merge pull request #138 from randomecho/chat-urls-untruncatification

Expand out URLs truncated from Campfire exports