Workaround for cutoff glyphs

There's an issue where drawing the cell backgrounds will overwrite part
of a neighboring glyph. The real solution here is to figure out glyph
metrics properly, but simply limiting to 2 draw calls per frame (first
background, then all the glyphs) makes the problem "go away".

src/renderer/mod.rs

@@ -378,7 +378,7 @@ impl Batch {
 }
 
 /// Maximum items to be drawn in a batch.
-const BATCH_MAX: usize = 4096;
+const BATCH_MAX: usize = 65_536;
 const ATLAS_SIZE: i32 = 1024;
 
 impl QuadRenderer {