Cargo Features

fplist has no features set by default.

[dependencies]
fplist = { version = "0.2.1", features = ["multithreaded", "serde_impls"] }
multithreaded
serde_impls = serde

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.

serde serde_impls?