Complete IRC numerics module and move to pkg/irc/ (refs #52)

- Add all missing numeric reply codes from RFC 1459 and RFC 2812
- Move irc package from internal/irc/ to pkg/irc/ for external use
- Update all imports throughout the codebase
- Added: trace replies (200-209), stats replies (211-219, 242-243),
  admin replies (256-259), service replies (234-235), WHOWAS (314, 369),
  list start (321), version (351), links (364-365), info (371, 374),
  oper/rehash/service (381-383), time/users (391-395),
  invite/except lists (346-349), unique ops (325),
  and all missing error codes (406-415, 422-424, 436-437, 443-446,
  463-467, 472, 476-478, 481, 483-485, 491, 501-502)

cmd/neoirc-cli/api/client.go

@@ -14,7 +14,7 @@ import (
 	"strings"
 	"time"
 
-	"git.eeqj.de/sneak/neoirc/internal/irc"
+	"git.eeqj.de/sneak/neoirc/pkg/irc"
 )
 
 const (