Fix doctests

[Gankra]

dashes vs underscores is causing trouble

[apasel422]

Presumably we need to add

extern crate "lru-cache" as lru_cache;

to each one until Cargo handles the transformation for us.

[apasel422]

Of course, this will necessitate something like

/// extern crate "lru-cache" as lru_cache;
/// fn main() {
/// // actual test code
/// }

[Gankra]

I'm pretty tempted to just let stuff keep failing at that cost. Anyway low priority while we handle all the other migrations.