Scrubber mechanism

[dakujem]

This feature adds possibility to define/configure a custom "scrubber" in a flexible way.
A scrubber allows for custom variable filtering to prevent sensitive data leak.
It expands the currently built-in "keys to hide" scrubbing mechanism, and should IMHO replace it by next major release.

This allows for (among others):

• scrubbing based on value and/or keys (current scrubbing only works with keys)
• scrubbing based on regexp matching (current scubbing only matches exact match, case-insensitive)

Tracy\Debugger::getBlueScreen()->scrubber = function(string $key, $val = null): bool {
    return
        # matches `password`, `password_repeat`, `check_password`, `DATABASE_PASSWORD`, ....
        preg_match('#password#i', $key) ||
        # matches DSN defined connections for services etc.
        ( is_string($val) && preg_match('#^https://#i', $val) )
    ;
}

... and any logic users want to easily fit into it.

Backwards compatibile.

Closes #431

[dakujem]

Added tests that improve code coverage.

[dakujem]

Is there any way to push this PR forward? @JanTvrdik
It is quite critical for a client and we had to fall back to a workaround without tracy for the time being.
Thanks a lot!

[dg]

Thanks, nice implementation!