Now matches Godot `master` target names and supports the same flags with
the following notable exceptions:
- The default target is "template_debug", since it's compatible with
editor builds (and TOOLS_ENABLED is never used internally).
- separate_debug_symbols is still not supported, and will be done in a
separate commit.
Works by executing project `SConstruct`s file in a cloned env (a bit
like Godot does for modules) so you don't have to worry about platform
and toolchain setup.
Convert the project test file to work as submodule, add it to CI
Run with:
```
scons build_projects=test,/path/to/other/project
```