Improve logging for Predicates

When using the predicate language, there is no debugging to speak of that lets you see

• What predicates were processed for a request
• What the result of each predicate was
• What handlers ran in what order

This request involves creating a new PREDICATE_LOGGER and has two main pieces:

• Add logging to the PredicatesHandler and some select predicates such as regex or paths to trace the flow of execution
• Create toString() methods to get useful text representations of all predicates, handlers, and exchange attributes commonly used in the predicate language

The string representation closely matches the actual predicate language itself, so the logs should be very readable.  

Example

Given the following predicate rules:

path-template('/foo/{bar}/{f}')->response-code(404)
path-suffix(.env)->response-code(404)
not regex( '.*\.(bmp|gif|jpe?g|png)' ) -> rewrite('/index.cfm%{RELATIVE_PATH}')

And an incoming request to

/main

The sample logging output to the PREDICATE_LOGGER with "trace" level enabled would be:

[TRACE] Predicate [path-template( '/foo/{bar}/{f}' )] resolved to false for HttpServerExchange{ GET /main}.
[TRACE] Predicate [path-suffix( '.env' )] resolved to false for HttpServerExchange{ GET /main}.
[TRACE] Predicate [ not regex( pattern='.*\.(bmp|gif|jpe?g|png)', value='%{RELATIVE_PATH}', full-match='false', case-sensitive='false' )] resolved to true. Next handler is [rewrite( '/index.cfm%{RELATIVE_PATH}' )] for HttpServerExchange{ GET /main}.
[DEBUG] Request rewritten to [/index.cfm/main] for HttpServerExchange{ GET /main}.