* Simplify build process
- Remove dependencies on DevkitPro
- Use linker similarly to min-gba
- Update cargo.toml so that dev builds will build
- Update cargo config so that std builds can run without the linker for
testing purposes
- Update CI flow to remove xbuild dependency
* Add windows toolchain install
* Add windows section to toolchain install instructions
* Remove cargo-xbuild dev dependency
As of Rust nightly 2020-07-15, we can set the default build target
and build-std feature of cargo instead of relying on cargo-xbuild.
Since the thumbv4-non-agb target is the default for all cargo commands,
change the Rust snippets in Makefile.toml to cross-platform duckscript.
The only uglyness we're left with is running the unit tests. We want to
build and run the tests on the host archetecture. Create three platform
overrides for Mac, Windows, Linux and set flags to override the default
target triple and build-std option.
* remove uneeded attribute
From cargo: "the feature `cfg_target_vendor` has been stable since
1.33.0 and no longer requires an attribute to enable"
