Previously, if running an instance on e.g. http://localhost:8080, the port
would show up in the Gopher links and potentially cause rendering to fail.
This fixes that.
This adds gopher support to WriteFreely -- both single- and multi-user
instances. It is off by default, but can be enabled with the new
`gopher_port` config value in the `[server]` section.
When enabled, multi-user instances will show all public blogs at
gopher://[host]:[gopher_port]/ -- otherwise, blogs are accessible at
gopher://[host]:[gopher_port]/[blog]/
This is just a proof of concept for now. We still need to handle some
edge cases and different configurations, like private instances.
Ref T559
