[addition] pattern to matching Modifiers / exporting Modifiers constructor

[epoberezkin]

Modifiers do not allow pattern matching - it makes code more complex than it could have been.

The change could be backwards compatible by defining and exporting pattern synonyms for Modifiers in addition to the existing functions.

pattern NoModifiers = Modifiers 0
pattern ShiftKey = Modifiers 1
pattern CtrlKey  = Modifiers 2
pattern AltKey   = Modifiers 4
pattern MetaKey  = Modifiers 8

Or, at the very least, it would help exporting Modifiers constructor so they can be defined in the code (e.g. if you don't want to use pattern synonyms extension).

Thank you