fix: finish meson porting and remove Makefiles and CMake files

[c-dilks]

Continuation of #58

After merging this, let's tag version 4.2.0 (as set in the new meson.build file).

Breaking Changes

• CMake users will need to use pkg-config for dependency resolution, as well as its targets

Noteworthy Changes

• executable names: meson gets confused when testing executable names that end in .exe; I've therefore removed the file extension, and added a prefix hipo_ (to mitigate name collisions)
• reaction.cc, found in extensions/julia/lib, has been moved to hipo4/, and built as part of libhipo4 (rather than separately in libjulia); this revealed a bug in fizika.h, where include directives were found inside the namespace
• lz4 submodule is removed
  • meson will first check the system for lz4, if it's not found, it will use the WrapDB, which will download it, build it locally, and use it
• Many remaining Makefiles require environment variables such as $HIPO and $PKG_CONFIG_PATH to be set
  • this can be done by sourceing the installed libexec/this_hipo.* file (depending on your shell)
  • these Makefiles could be converted to meson, but that can be a job for another PR
  • WARNING: these Makefiles are NOT tested!

Downstream PRs:

• ci: test HIPO 4.2.0 JeffersonLab/clas12root#75
• ci: HIPO 4.2.0 testing JeffersonLab/iguana#270

[c-dilks]

@gavalian This isn't ready to be merged yet, since it needs more testing and debugging. I'll let you know when it's ready.

[gavalian]

Looks (and sounds) good.