dev-libs/msgpack: version bump to 1.4.2 and 2.2.1

dev-libs/msgpack: version bump to 1.4.2 and 2.2.1

An update to the latest version of 1.X and 2.X of the package. This was
already being worked on in PR #2974, I processed the comments and added
some extra things:

* Updated copyright.
* EAPI version bump.
* Updated license to Boost-1.0.
* Added examples USE-flag.
* Added doc USE-flag.
* Updated patches for cflags and static-libs.
* Masked for testing.

The new versions are masked for testing as the status of depending packages is
currently unknown. Bugs for the package maintainers will be created.

Gentoo-Bug: https://bugs.gentoo.org/601370
Closes: https://github.com/gentoo/gentoo/pull/4078
Package-Manager: Portage-2.3.6, Repoman-2.3.1