Add Titan support

[davep]

Adds support for uploading data using Titan. Also adds support for the ;edit extension to Titan.

TODO:

• Add a "rich input/upload" dialog, that's like the user input interface but allows for attached files, setting the mime type, etc.
  • Allow calling out to $EDITOR to enter the free text
• Add the actual handler code.
• Confirm if a response to a Titan upload can be a 6x
• Add support for the ;edit extension to Titan
• Add a protocol page in the documentation.
• Update protocol lists in the README, docs, GitHub page, etc, to include Titan.
• Attempting to upload a file bigger than BBS allows (as a test) causes Rogallo to freeze and never come back. Investigate and fix.

Closes #355.