New features

Renaming now supports names involving inherit.
- Renaming identifiers inside inherit will change the definition, and
  foo: { inherit foo/* -> new */; }
  =>
  foo: { new = foo; }
- Renaming identifiers outside inherit will change references.
  foo/* -> new */: { inherit foo; }
  =>
  new: { foo = new; }
Show documentations during completion for builtins.

Currently only global builtins like map are supported.
The documentations are generated from Nix at build-time, and some
builtins don't have upstream documentations.
Hover. textDocument/hover
- Show documentations for global builtins.
- Show the kind of names, like let-bindings, parameters, or etc.
Syntax errors are now shown by default.
Custom diagnostics filter.

See docs/features.md for more information.
Symbol hierarchy, aka. outline. textDocument/documentSymbol
File formatting via external command. textDocument/formatting

Fixes

Contextual keyword or are now semantically highlighted correctly.
Parser error recovery is improved, and error messages are tweaked to be
more helpful.