docs: New documentation using mdbook (#471)

* docs: mdbook init

* Separate sub-options into their section

* docs: enable fold

* docs: merge core options into a single section

* doc generation: fix submodules index pages

* docs: add contributing section

* docs: rename 'core' group to 'Neovim Options'

docs: removed the index pages of empty sections

docs: remove obsolete 'mergeFunctionResults' function

* docs: use nix syntax highlighting

* docs: point to the new repo url

* docs: use recursive generation
docs: split submodules into subsections

* docs: fix contributing separator
docs: fix missing submodules docs

plugins/filetrees/neo-tree.nix

@@ -317,7 +317,7 @@ in {
           - values are lua code defining the callback function.
 
           Example:
-          ```
+          ```nix
           {
             before_render = \'\'
               function (state)
@@ -626,7 +626,7 @@ in {
           mappings =
             mkMappingsOption
             ''
-              ```
+              ```nix
                 {
                   "<space>" = {
                     command = "toggle_node";
@@ -679,7 +679,7 @@ in {
         };
       filesystem = helpers.mkCompositeOption "Filesystem options" {
         window = mkWindowMappingsOption (lib.mdDoc ''
-          ```
+          ```nix
             {
               H = "toggle_hidden";
               "/" = "fuzzy_finder";
@@ -747,7 +747,7 @@ in {
             Hide by pattern.
 
             Example:
-            ```
+            ```nix
               [
                 "*.meta"
                 "*/src/*/tsconfig.json"
@@ -808,7 +808,7 @@ in {
 
             Either use a list of strings:
 
-            ```
+            ```nix
             findArgs = {
               fd = [
                 "--exclude"