* gotcl_test.go: Added unit test file for use with 'go test' command.
  For now there are just a few tests for interp.ParseBraceWord

* gotcl.go: Arguments to procs now have type Arg, when defining new
  command you can give them a default value.  The 'proc' command will
  set these up appropriately.* gotcl_test.go: Added unit test file for use with 'go test' command.   For now there are just a few tests for interp.ParseBraceWord