v1.6.0: Control highlighting from the command line

With this release you can control highlighting from the command line:

  moar -colors=16 -style=arduinoxx moar.go

Available styles listed here:
  https://xyproto.github.io/splash/docs/longer/all.html

Also, you can now pass command line arguments through the environment,
good if you like some non-default theme:

  export MOAR="-colors=16 -style=arduinoxx"
  moar moar.go

If you put that export line in some init file, moar will always use your
favorite theme.