Cargo Features

rtdlib has no features set by default.

[dependencies]
rtdlib = { version = "1.8.1", features = ["sys"] }
sys = rtdlib-sys

Features from optional dependencies

In crates that don't use the dep: syntax, optional dependencies automatically become Cargo features. These features may have been created by mistake, and this functionality may be removed in the future.

rtdlib-sys sys?