This DRYs up functionality, pulling some of the complexity out of othermethods.Co-authored-by: Kate Higa <khiga8@github.com>

This simplifies tests: testing less for side-effects.Co-authored-by: Kate Higa <khiga8@github.com>

BREAKING CHANGEThe code for handling eventlistening is very trivial, and might vary perconsumer of this library. It is not core functionality, and should beleft to upstream to setup.Removing this reduces the API surface area and complexity from this libraryas it doesn't need to concern itself with event management and keyboardshortcuts.Co-authored-by: Keith Cirkel <keithamus@users.noreply.github.com>

BREAKING CHANGEThis was never used upstream, so we want to remove this in the interestof simplicity.Co-authored-by: Kate Higa <khiga8@github.com>

Without any event listeners (onCopy and keydown have been removedprior) AbortController is effectively dead code and can be removed.Co-authored-by: Keith Cirkel <keithamus@users.noreply.github.com>

Now that all functions can be used independently of `install()`, andoptions can be passed into those methods, it makes little sense to havethem in `install()`, and so it can be simplified to just providing thefunctionality of collecting containers.Co-authored-by: Keith Cirkel <keithamus@users.noreply.github.com>

BREAKING CHANGE`install(container)` was side-effectful behavior which determined wherequote containers would be. A better design for this is to have functionsrequire a `containerSelector` to query against. This does the same thingbut is slightly more idiomatic.Co-authored-by: Keith Cirkel <keithamus@users.noreply.github.com>

This boolean was useful for onCopy but is no longer useful.Co-authored-by: Keith Cirkel <keithamus@users.noreply.github.com>

This was only used to intercept quote behaviour, and doesn't really addany value as whatever used to listen to this can simply do the samebehaviour after `quote()` has been called.Co-authored-by: Keith Cirkel <keithamus@users.noreply.github.com>

`quote` really does very little, it effectively calls `extractQuote()`followed by `insertQuote()`. Both can be exported functions and couldbe used instead, providing more flexibility.Co-authored-by: Keith Cirkel <keithamus@users.noreply.github.com>

We can remove `getSelectionContext` entirely, by inlining it into the`extractQuote` body, however it was useful to pass in a custom selectioncontext for the use case of selecting the contents of an element.By introducing `quoteElement` as an option we can supply the single usecase for creating custom `SelectionContext`s, which also can replacesome code we have upstream.

BREAKING CHANGE`extractQuote` would be guaranteed to return `undefined` if`containerSelector` was not provided as an option, which means it is notoptional, and so should be an argument proper, as opposed to somethingin an options bag. This changes extractQuote to do just that.Co-authored-by: Kate Higa <khiga8@github.com>

The initial code created the `focusNode` const which was a differentname to the property it was retrieving: `startContainer`. Thissimplifies the code by making it more readable: less inventive namesprovides clearer intent as to the data manipulation that is happening.Co-authored-by: Kate Higa <khiga8@github.com>

The `quoteMarkdown` option of `extractQuote` was a "mode" -significantly changing the behaviour of the `extractQuote` function. Assuch it is better to split it out into a separate function which can beinvoked by client code - more explicit than setting an option.Co-authored-by: Keith Cirkel <keithamus@users.noreply.github.com>

This drastically simplifies the `asMarkdown` function, avoiding theawkward try/catch and throwing on a setTimeout. The callback is also afar more idiomatic pattern for intercepting objects for mutation.Co-authored-by: Keith Cirkel <keithamus@users.noreply.github.com>

BREAKING CHANGEThis function only ever used the `quoteElement` option, so it issimpler to have this as an optional argument as opposed to having anoptions object passed in.Co-authored-by: Kate Higa <khiga8@github.com>

Introduce `quotedText` to `Quote`.

Update `asMarkdown` type to always return `Quote`.