Working directories are now set seperately from the commands so they
can later be swapped out when running linters over projects is
supported, and also better support filename mapping for running linters
on other machines in future.
* Rust Cargo linter: Improve workspace support
When using Cargo workspaces [1], there is a 'Cargo.toml' directory in a
top level directory, listing all the crates in the project. If we are
currently editing one of the crates, 'cargo build' should execute in
that directory for that crate's separate `Cargo.toml`, otherwise Cargo
may spend more time possibly rebuilding the entire workspace, and maybe
failing on one of the other crates, instead of succeeding on the current.
[1] https://doc.rust-lang.org/book/second-edition/ch14-03-cargo-workspaces.html
* 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
