EU::ParseXS: Code cleanup

General refactoring to make the code (marginally) easier to follow
and more consistent. This should not result in a change in behaviour.
Includes version bump to 3.24.
Maintainers.pl: Refer to recent EU::ParseXS release
note that the ~~ operator is experimental

(cherry picked from commit 43c6e0a7ba1950c4a64b59be5d0a9cd7b1807cca)
officially discourage the use of threads

some language borrowed from a larger patch by Christian Walde
Upgrade CPAN::Meta from version 2.140630 to 2.140640
Update META files and remove blead customizations following previous commit

(The customizations were added to "fix" failures caused by the previous
upgrade of CPAN::Meta. This upgrade reverts the offending parts, so those
"fix"es can now be reverted too.)