Document some basic menu.hjson stuff

docs/menu_system.md

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+# Menu System
+ENiGMA½'s menu system is highly flexible and moddable. The possibilities are almost endless! By modifying `menu.hjson` you will be able to create a custom look and feel unique to your board.
+
+## The Basics
+Like all configuration within ENiGMA½, menu configuration is done via a HJSON file. This file is located in the `mods` directory: `mods/menu.hjson`.
+
+Each entry in `menu.hjson` defines an object that represents a menu. These objects live within the `menus` parent object. Each object's *key* is a menu name you can reference within other menus in the system. 
+
+## Example
+Let's look a couple basic menu entries:
+
+```hjson
+telnetConnected: {
+  art: CONNECT
+  next: matrix
+  options: { nextTimeout: 1500 }
+}
+```
+
+The above entry `telnetConnected` is set as the Telnet server's first menu entry (set by `firstMenu` in the server's config).
+
+An art pattern of `CONNECT` is set telling the system to look for `CONNECT<n>` in the current theme location, then in the common `mods/art` directory where `<n>` represents a optional integer in art files to cause randomness, e.g. `CONNECT1.ANS`, `CONNECT2.ANS`, and so on. You can be explicit here if desired, by specifying a file extension.
+
+The entry `next` sets up the next menu, by name, in the stack (`matrix`) that we'll go to after `telnetConnected`.
+
+Finally, an `options` object may contain various common options for menus. In this case, `nextTimeout` tells the system to proceed to the `next` entry automatically after 1500ms.
+
+Now let's look at `matrix`, the `next` entry from `telnetConnected`:
+```hjson
+matrix: {
+  art: matrix
+  form: {
+    0: {
+      VM: {
+        mci: {
+          VM1:  {
+            submit: true
+            focus:  true            
+            items: [ "login", "apply", "log off" ]
+          }
+        }
+        submit: {
+          *: [
+              {
+                  value: { 1: 0 }
+                  action: @menu:login
+              }
+              {
+                  value: { 1: 1 },
+                  action: @menu:newUserApplication
+              }
+              {
+                  value: { 1: 2 },
+                  action: @menu:logoff
+              }
+          ]
+        }
+      }
+    }
+  }
+}
+```
+
+In the above entry, you'll notice `form`. This defines a form(s) object. In this case, a single form by ID of `0`. The system is then told to use a block only when the resulting art provides a `VM` (*VerticalMenuView*) MCI entry. `VM1` is then setup to to `submit` and start focused via `focus: true` as well as have some menu entries ("login", "apply", ...) defined.
+
+The `submit` object tells the system to attempt to apply provided match entries from any view ID (`*`). Upon submit, the first match will be executed. For example, if the user selects "login", the first entry with a value of `{ 1: 0 }` or view ID 1, value 0 will match causing `action` of `@menu:login` to be executed (go to `login` menu).