* When working on rust/cargo projects of varying sizes, it may be useful
to either build all possible features (i.e. lint all possible
conditionally compiled code), or even turn off other features for a
quicker edit-lint cycle (e.g. for large projects with large build times)
* Added a g:ale_rust_cargo_default_feature_behavior flag for instructing
cargo to not build any features at all (via `--no-default-features`),
building default features (via no extra flags), or building all possible
features (via `--all-features`)
* Also added a g:ale_rust_cargo_include_features flag for including
arbitrary features to be checked by cargo. When coupled with
g:ale_rust_cargo_default_feature_behavior this allows for full
customization of what features are checked and which ones are ignored
