Sherman — a truly monstrous tree type

It turns out that in the production of an editor, sometimes specialized data structures are used. Sometimes data structures are similar enough that they can be united into a single abstract type, with parameterizations to suit the original needs. This crate primarily exports a single type -- RleTree -- which represents the collection of all features

Notable features

• Values are retrieved by global index
• RleTree is named such for its run-length encoding -- individual entries in the tree represent a uniform range of indexes
• Efficient "shift" operations -- the details of the run-length encoding allow new ranges to be inserted in the middle, shifting everything after them, in O(log n) time
• Node references -- the position and values of a prior insertion can be fetched in O(log n) time, with relatively little overhead
• Lock-free concurrent {copy,clone}-on-write -- RleTrees can be shared across threads, with concurrent writes copying or cloning only the path down to the changed node(s).

And of course, all of these features are zero-cost when not in use: the tree is constructed in such a way so that only the instances that actually do use these extra feature (like node references or concurrent COW) have to pay the cost of them. And the cost of each individual feature has been minimized as much as is possible.

For a more detailed explanation on how we're able to pull this off, ARCHITECTURE.md gives a high-level overview of all the moving pieces to this crate.

Naming

This library is named after General Sherman, a tree in Sequoia National Park that is the current largest tree Earth by volume.