Cargo Features

mml has no features set by default.

mml = { version = "0.1.41", features = ["travis", "unstable", "lints", "nightly"] }
travis = lints, nightly
debug fn-emilgardis implem unstable
lints travis? = clippy, nightly
nightly lints? travis?

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.

clippy lints?