This patch updates the CLI to use anyhow and thiserror for error
management. The main feature that our custom `Error` type was providing
was a _list_ of messages, which would allow us to annotate "lower-level"
errors with more contextual information. This is exactly what's
provided by anyhow's `Context` trait.
(This is setup work for a future PR that will pull the `config` and
`loader` modules out into separate crates; by using `anyhow` we wouldn't
have to deal with a circular dependency between with the new crates.)
Right now this is just used for two things:
* Specifying folders for locarting parsers to use with `tree-sitter
parse` and `tree-sitter highlight`
* Specifying colors to use for `tree-sitter-highlight`
When there are embedded documents, multiple scopes can start or
end at the same position. Previously, there was no guarantee that
the ScopeEnd events would always occur in the reverse order of the
ScopeStart events. The easiest way to avoid exposing inconsistency
is to not surface the scopes being ended.
