Neovim version 0.5 [1] is a long-time awaited update that introduces
features like tree-sitter [2][3] support and native LSP [4][5].
Even though Neovim devides more and more from Vim through specific
features like first-class Lua support with custom APIs, the highlighting
for tree-sitter is achived through "normal" syntax highlighting groups.
Most of the groups are already linked by the nvim-treesitter plugin by
default [6] so only a few groups have been adjuated for now to fit the
Nord style.

[1]: https://github.com/neovim/neovim/releases/tag/v0.5.0
[2]: https://github.com/tree-sitter/tree-sitter
[3]: https://github.com/nvim-treesitter/nvim-treesitter
[4]: https://neovim.io/doc/user/lsp.html
[5]: https://github.com/neovim/nvim-lspconfig
[6]: https://github.com/nvim-treesitter/nvim-treesitter/blob/90f15d9/plugin/nvim-treesitter.vim

Co-authored-by: Ferran Jovell <[email protected]>
Co-authored-by: Arctic Ice Studio <[email protected]>
Co-authored-by: Sven Greb <[email protected]>

Closes GH-235

Add support for `vim-pandoc/vim-pandoc-syntax`

To improve syntax highlighting for Pandoc [1], support for the
vim-pandoc/vim-pandoc-syntax [2] plugin has been implemented.
Most groups are linked to existing Markdown groups to ensure a
consistent style across languages and different plugins.

Configurations used for testing:

```vim
let g:pandoc#syntax#conceal#cchar_overrides = {"atx": "〉"}
let g:nord_italic = 1
```

Resources:

- `g:pandoc#syntax#conceal#cchar_overrides` docs [3]
- `s:cchars` definition [4]
- Markdown "Extended Syntax" Guide [5]

[1]: https://pandoc.org
[2]: https://github.com/vim-pandoc/vim-pandoc-syntax
[3]: https://github.com/vim-pandoc/vim-pandoc-syntax/blob/68d7249/doc/pandoc-syntax.txt#L45-L50
[4]: https://github.com/vim-pandoc/vim-pandoc-syntax/blob/5056e63/syntax/pandoc.vim#L37-L72
[5]: https://www.markdownguide.org/extended-syntax

Co-authored-by: Arctic Ice Studio <[email protected]>
Co-authored-by: Sven Greb <[email protected]>

Closes GH-220

Support for LSP code lenses

Before LSP code lenses [1] where code lenses were highlighted with the
default color which has been changed to make it less visually intrusive,
like other UI related elements, i.e. messages of linters.

[1]: https://neovim.io/doc/user/lsp.html#lsp-highlight-codelens

GH-266


Co-authored-by: Arctic Ice Studio <[email protected]>

The `TSError` group is used to highlight syntax/parser errors [1] which
caused an aggressive styling where the background color of many syntax
elements was rendered with `nord11` during typing. This was caused due
to the fast processing of `tree-sitter` which also resulted in highlight
flickering.
This is a known problem and was fixed by many other themes (e.g. Dracula
[2]) by removing the group again. One of the core maintainers of
`nvim-treesitter` provided a solution by remapping groups [3] and also
mentioned that the group is styled by the `nvim-treesitter` plugin but
the active theme [4].

Syntax errors can still be highlighted through linters and parsers like
Neovim's LSP [5] can still be used instead to highlight errors with the
correct style (e.g. only change the foreground color of a single word).

[1]: https://github.com/nvim-treesitter/nvim-treesitter/blob/fb5d6e04/doc/nvim-treesitter.txt#L493-L495
[2]: dracula/vim#232
[3]: nvim-treesitter/nvim-treesitter#78 (comment)
[4]: nvim-treesitter/nvim-treesitter#1016 (comment)
[5]: https://github.com/neovim/nvim-lspconfig

Fixes GH-269