[WIP] History API rework

[ClementNerma]

NOTE: This PR is a work-in-progress, and is not ready to be merged as-is. There are ongoing discussions about the new API design.

This PR aims to overhaul the history API of reedline in order to make it usable outside of the crate. It also aims to make it more robust, more intuitive and less error-prone.

Following discussions in #680 (original PR), #735 (discussion), also embedding future discussions for #746.

For newcomers in the discussion, please read #680 first, as it will help you understand the motivations and existing discussion behind this PR.

TODO list (includes unvoted tasks):

• Global API rewrite
• Introduce a new, fast history backend with all available features (e.g. sled-backed?)
• Remove the sync API (see Sync history after each insert #746)
• Add new documentation and add integration examples
• Move the History::session method someplace else (to move session detection logic outside of the history implementation)

cc @stormasm @fdncred @sholderbach