As a result
- The error messages will now show the error with `-` instead of `_`
- The LSP will auto-complete with -
- The interpreter's list of properties will list the property with '-'
(but we made the change so that set_property, get_property, and so on
work also if passed a '-')
Add support for built-in property aliases and rename `color` to
`background` - in preparation for it also changing to type brush.
Right now the alias is silent, a deprecation and overall change
will come in a subsequent change.
