`BooleanType` should be logical, not a value, for consistent expression grammar

[gregsdennis]

This is another option to resolve #387 (see #395 for the first option).

For this, BooleanType is not a value but represents the logical result of test-expr.

• Provides for functions that can return a true or false result by declaring that such a result is logical, not JSON.
• Removes OptionalBooleanType is no longer necessary, as Nothing in a test-expr behaves the same as logical false.

A fallout of this is that $[?match(@.timezone, 'Europe/.*')==false] is not valid/well-formed.

[gregsdennis]

There are a few editorial changes to make too

Yeah, I noticed few unrelated editorials I'd like to rework as well.

[gregsdennis]

Closing this in favor of ☝️ as it's more complete.