maintain the initial font size in a global

Apps should keep the global updated when changing the font size.

main.lua

@@ -36,6 +36,8 @@ function App.initialize_globals()
   -- blinking cursor
   Cursor_time = 0
 
+  Font_height = 20
+
   -- for hysteresis in a few places
   Current_time = 0
   Last_focus_time = 0  -- https://love2d.org/forums/viewtopic.php?p=249700
@@ -112,8 +114,8 @@ function load_settings()
     App.screen.move(settings.x, settings.y, settings.displayindex)
     if on.load_settings then on.load_settings(settings.app) end
   else
-    local font_height = 20
-    love.graphics.setFont(love.graphics.newFont(font_height))
+    Font_height = 20
+    love.graphics.setFont(love.graphics.newFont(Font_height))
     local os = love.system.getOS()
     if os == 'Android' or os == 'iOS' then
       -- maximizing on iOS breaks text rendering: https://github.com/deltadaedalus/vudu/issues/7

reference.md

@@ -21,6 +21,10 @@ two categories.
   * `flags` -- some properties of the app window. See [`flags` in `love.graphics.getMode`](https://love2d.org/wiki/love.window.getMode)
     for details.
 
+* `Font_height` -- remembers the current font height on initialization. But
+  you're responsible for setting it when updating font height. (Think of this
+  as the body font, but apps so far assume a single font size.)
+
 ## Functions you can implement that will get automatically called
 
 * `on.initialize(arg)` -- called when app starts up. Provides in `arg` an
@@ -237,6 +241,9 @@ early warning if you break something.
   this for the most part, just run it after loading or modifying
   `state.lines`.
 
+* `edit.update_font_height(state, font_height)` -- updates all state dependent
+  on font height.
+
 If you need more precise control, look at the comment at the top of
 `edit.initialize_state` in edit.lua. In brief, the widget contains an array of
 `lines`. Positions in the buffer are described in _schema-1_ locations