Add CLI option for the server port.

src/short_url.nim

@@ -8,7 +8,8 @@ Usage:
 
 Options:
 
-  -c, --config <cfgFile>    Use the given config file (defaults to ./short-url.cfg.json)
+  -c, --config <cfgFile>    Use the given config file (defaults to ./short_url.cfg.json)
+  --port <port>             Bind the server to the given port (defaults to 80)
   --debug                   Enable debug-level logging.
   --trace                   Enable trace-level logging (takes precedence over --debug).
 """
@@ -29,7 +30,7 @@ type
 proc loadConfig(args: Table[string, Value]): ShortUrlsConfig =
   let cfgFile =
     if args["--config"]: $args["--config"]
-    else: findConfigFile("short-url.cfg.json")
+    else: findConfigFile("short_url.cfg.json")
 
   result.cfg = initCombinedConfig(filename = cfgFile, docopt = args)
   result.port = parseInt(result.cfg.getVal("port", "80"))