Cleanup of old code/TODOs
Checks that a road can be built
Added pretty-printing for edges/vertices

Both are identified by writing the letter of an adjacent cell, followed by a
number from 1 to 6, indicating which vertex/edge of the cell is being used.
Fixed server bugs, added a 3-user test

catan-server.rkt now assumes exactly 3 users will connect. It assigns them
initial settlements and roads. There are currently some bugs that need to be
fixed, but for now the next step is to change the engine so that formatted
responses are sent to the client, instead of raw strings.
Mostly got server/client interaction working

I made the server send formatted messages to the client, rather than raw
strings. I fixed several bugs in the client/server implementation, and made it
more robust. Next step is to implement say, and to make the client parse user
input, and format it for the server.
Implemented say
Made client smart

It now parses input from the user, and sends only valid commands to the server.
It also accepts the nicer 3-character format for specifying edges and vertices.
minor client bug fix
Fixed initial test positions in catan-server.rkt

Initial testing positions are now valid.
Fixed can-road? boundary edge bug
Added more functionality to show
Implemented bank
Fixed substring bug in client
Made initial settlements/roads work for up to 3
Fixed bugs where users could act out of turn
Added a response lock to the state

Currently nothing uses it, but the rlock exists.
misc