Port JQ to Meson build system

[Salamandar]

Hi, this is a suggestion to port jq to the Meson build system.
(small disclaimer, i was a meson contributor back in ye old days and I'm the one who ported Gimp to Meson)

So, the upsides are:

• A slightly faster and more comprehensible configure (meson setup <build dir> instead of autoreconf -i ; ./configure) and more discoverable (meson_options.txt).
• An out-of-build build by default
• An advance build system automatically providing sanitizers, unity builds, easy to use build profiles (release, debug etc)
• ~560 lines autoconf+automake to ~400 lines meson

downsides are:

• Meson only supports subprojects in the subprojects subdirectory, so for "builtin" oniguruma to be included, the vendor directory should be renamed.