Check window width and height for focus_max_or_equal

At present it only checks for window width, which works for vertical splits.
However, horizontal splits will not properly maximise since they will always
have the max width, so attempts to focus_max_or_equal will always lead to
focus_equalise.

lua/focus/modules/functions.lua

@@ -44,7 +44,9 @@ end
 
 M.focus_max_or_equal = function()
     local winwidth = vim.fn.winwidth(vim.api.nvim_get_current_win())
-    if winwidth > vim.o.columns / 2 then
+    local winheight = vim.fn.winheight(vim.api.nvim_get_current_win())
+    local bigger_than_half = (winwidth > vim.o.columns / 2) and (winheight > vim.o.lines / 2)
+    if bigger_than_half then
         M.focus_equalise()
     else
         M.focus_maximise()