Add Meson build support

[kennethdhau]

Added meson project files, maintaining compilation/linking flag consistency with base Makefile (exception of new addition of -flto by default)

Included tests from ./test-high and ./test-low as Meson tests

Edited README.md to reflect usage

[kennethdhau]

The Meson in the test-high/test-low directories could be seriously cleaned up, but I left it all explicit in case there were any per-test tweaks that seemed appropriate. If it's too unwieldy or not maintenance-friendly, I can make the change.

Sorry for the commit spam.