[plugins] director: make director enabled state persistent
changelog updates
CustomData: be a struct, not a class.
mysql_config seems to propagate -fabi-version as cflags. we really don't want that
[plugins] director: only load director.enabled from db if it actually exists (soft migration)
director's app_cluster.db test file update
[plugins] director: refactor code to expose RequestNotes to other flow exposed functions, too.

We required that to allow things like custom flow functions to disable
object caching, for example.

This refactorization however still makes sense, as we now deal with one
handle internally for to-be-served HTTP requests: RequestNotes.

We may come up with a better name later.
[plugins] director: enables director.cache.bypass() flow function
[http] HttpStatus: typo fix for 'GatewayTimeout'
[plugins] director: shaper token allocation cleanup
[http] flow API: added read-property `req.query`.

will return the request query args
[plugins] director: minor code cleanup
[base] LogMessage: fixed isDebug()
improved debug logging and log message filtering / highlighting.

This is to help improving debugging sessions.
It introduces the optional environment variable XZERO_DEBUG
that can contain a colon seperated list of tag specifications
used to only show debug messages of that tag name, its
optionally defined verbosity level and in its optionally
specified ANSII color (helpful when logging into a terminal).

If no XZERO_DEBUG is specified et al but logging debug was requested
(via --log-severity), then every debug message is logged.

Example:

    XZERO_DEBUG="worker/3/green:director/10/white:director-cache/10/bold/yellow/bg-red:misc"
    export XZERO_DEBUG
    ./src/x0d ...
[plugins] director: debugging slightly improved
[plugins] director: new flow property: director.cache.key
[plugins] director: compile fix for cache disabled mode
compile fix for old compilers. too bad. :(
better detect proper llvm-config* binary
typofix in pkg-config file for XzeroBase