build: Support many other buildsystems

[obiwac]

This is the comment about this in #50:

Already support building simple setups with other build systems, I'm notably thinking of Meson/Ninja as is quite popular nowadays, CMake, bmake/gmake (how can we automatically detect this? default to gmake and only use bmake if e.g. a FreeBSD port makefile is detected?), ./configure, Premake, Cargo (which will completely replace the RustC class), and Go.

And here is the pre-v0.2.0 comment:

It's annoying to have to look up how random buildsystem #61345 works when building a new project - it'd be much more ergonomic to just be able to bob build everything.

These are the buildsystems I'd like to support:

• build.~wren~fl (naturally 😏)
• Regular makefiles (how to differentiate between BSD & GNU make and run bmake/gmake accordingly?)
• CMake
• Meson/Ninja
• QMake
• autoconf
• setup.py/pyproject.toml
• cargo
• npm (could npx next * be run automatically if detected to be a Next.js project?)

There's also the question of whether or not these should all be built in to Bob, or if there should be some kind of "plugin" system.
These plugins could be basic Wren scripts which have a check function to check whether or not a project matches its buildsystem, and then build/install/run functions for the various instructions.

This is now done using bsys' ("build systems"), and the check function is called probe. Plugins sound like too much work/fuss/complexity when, well, it's just a build system.