Update PowershellSyntax.tmLanguage

Fixes several issues:
**229**: Correctly highlights the operators ```-clt```, ```-cle```, ```-cgt```, ```-cge```
**235**: Fixes issues highlighting paths with symbols in them
**259** & **265**: Fixes issues with operator highlighting, such as ```-NoTypeInformation``` being incorrectly highlighted as two elements, but allows for ```-Not1``` to be correctly interpreted as two elements
**393**: Allows for permissible symbols in command names
What is the meaning of `?!\p{L}` ? Can it be replaced with `\b` (word boundary)