--debug option for printing debug info

[athos]

Resolves #9.

After this being merged, Trenchman prints debug info (i.e. messages communicated between the client and server) with the —debug option:

$ trench --debug
[DEBUG:SEND] map["id":"init" "op":"clone"]
[DEBUG:RECV] map["id":"init" "new-session":"cee88e31-b813-4fd4-8fc2-33fa085c7a0c" "session":"none" "status":["done"]]
[DEBUG:SEND] map["op":"describe"]
[DEBUG:RECV] map["id":"unknown" "ops":map["clone":map[] "close":map[] "complete":map[] "describe":map[] "eldoc":map[] "eval":map[] "info":map[] "load-file":map[] "lookup":map[] "ls-sessions":map[]] "session":"none" "status":["done"] "versions":map["babashka":"0.8.156" "babashka.nrepl":"0.0.6-SNAPSHOT"]]
user=> (map inc [1 2 3])
[DEBUG:SEND] map["code":"(map inc [1 2 3])" "id":"a524995d-a048-4b43-869a-db23185c90c4" "ns":"user" "op":"eval" "session":"cee88e31-b813-4fd4-8fc2-33fa085c7a0c"]
[DEBUG:RECV] map["id":"a524995d-a048-4b43-869a-db23185c90c4" "ns":"user" "session":"cee88e31-b813-4fd4-8fc2-33fa085c7a0c" "value":"(2 3 4)"]
[DEBUG:RECV] map["id":"a524995d-a048-4b43-869a-db23185c90c4" "session":"cee88e31-b813-4fd4-8fc2-33fa085c7a0c" "status":["done"]]
(2 3 4)
user=>