Pretty docstrings

[aspeddro]

1. Add ```rescript metadata to codeblocks

   • I'm working on docgen and some pages don't have syntax highlighting, Belt API page

2. Rename metadata from ```res example to rescript

   This change is for LSP clients to apply syntax highlighting for hover/signatureHelp, see Improving doc comments syntax highlighting in hovering rescript-vscode#545

   Neovim use the codeblock metadata to apply syntax highlight through tree-sitter parser feat(lsp): use treesitter for markdown floating windows neovim/neovim#25073

3. Add ## Examples header

4. Remove deprecated comments, use attr @deprecated

5. Dedent comments

6. Update ocaml comments to rescript format

I'll keep this as a draft and test it with the docgen