Fix inline URLs in documentation comments

Add missing documentation

Split implementation of `SelectSettings` algorithm into separate sub-modules for easier testing

Add basic tests for `fn select_settings(…)`

Move tie-breaking policies into separate sub-module

Extract `fn select_settings_candidates(…)` variant without tie-breaking from `fn select_settings(…)`

Make functions accept `IntoIterator` rather than `Iterator`, where appropriate

Rename `SelectSettingsPolicy` to `TieBReakingPolicy`

Make `fn select_settings(…)` accept `IntoIterator` rather than `Iterator`

Remove `SettingFitnessDistanceErrorKind::Invalid` error variant

Make `fn generate_overconstrained_error()` return more detailed error message.

cons

Add a `SelectIdealSettingsPolicy ` settings selection policy

Add a naïve `SelectFirstSettingsPolicy` settings selection policy

Make `fn select_settings(…)` accept an iterator of borrowed `MediaTrackSettings` items

Add implementation of 'SelectSettings' algorithm