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/languages/nvim-jdtls.nix

@@ -21,7 +21,7 @@ in {
         You should either set a value for this option, or, you can instead set the `data` (and
         `configuration`) options.
 
-        ```
+        ```nix
         plugins.nvim-jdtls = {
           enable = true;
           cmd = [
@@ -34,7 +34,7 @@ in {
         ```
 
         Or,
-        ```
+        ```nix
         plugins.nvim-jdtls = {
           enable = true;
           data =  "/path/to/your/workspace";

plugins/languages/sniprun.nix

@@ -36,7 +36,7 @@ in {
           only sucessful runs (or errored-out runs respectively)
 
           Example:
-          ```
+          ```nix
           [
             "Classic"                    # display results in the command-line  area
             "VirtualTextOk"              # display ok results as virtual text (multiline is shortened)

plugins/languages/vim-slime.nix

@@ -53,14 +53,14 @@ in
 
           Examples:
             - `tmux`:
-              ```
+              ```nix
                 {
                   socket_name = "default";
                   target_pane = "{last}";
                 }
               ```
             - `zellij`:
-              ```
+              ```nix
                 {
                   session_id = "current";
                   relative_pane = "right";