support conditional breakpoints

[weinand]

extend the debug protocol to support conditional breakpoints (and other additional breakpoint attributes).

[weinand]

fyi @isidorn

[isidorn]

@weinand looks good but why call it expression and not condition

[weinand]

@isidorn good question. Probably because the corresponding argument to the "evaluate" request is called "expression" too. But you are right, we should change this to condition.

[weinand]

@isidorn I've pushed the name change

[isidorn]

Thanks will adopt it right now