Added support for string vars on commands that require a string

- Fixes bugreport:7901, thanks to Angelmelody
  http://hercules.ws/board/tracker/issue-7901-about-pass-variable-type-as-function-parameter
- Bonus: debugmes can now take both strings and numbers (i.e. to print a
  number variable you no longer need to do 'debugmes "" + .@num;')

Signed-off-by: Haru <haru@dotalux.com>