Canonical definitions of home_dir, cargo_home, and rustup_home.
This provides the definition of home_dir used by Cargo and rustup,
as well functions to find the correct value of CARGO_HOME and
RUSTUP_HOME.
The definition of home_dir provided by the standard library is
incorrect because it considers the HOME environment variable on
Windows. This causes surprising situations where a Rust program will
behave differently depending on whether it is run under a Unix
emulation environment like Cygwin or MinGW. Neither Cargo nor rustup
use the standard libraries definition - they use the definition here.
This crate further provides two functions, cargo_home and
rustup_home, which are the canonical way to determine the location
that Cargo and rustup store their data.
See rust-lang/rust#43321.
MIT OR Apache-2.0