message: Rewrite clear screen to use mkArray
  No big reason, only the assignment to an array initialized to [] looks like an out
  of bounds access (it's not but looks surprising to me)
diff: @@ -2,6 +2,7 @@ import { fs } from '../electronImports';
  import { framebufFromJson } from '../../redux/workspace';
  import { DEFAULT_BACKGROUND_COLOR, DEFAULT_BORDER_COLOR } from '../../redux/editor';
  import { Pixel } from '../../redux/types';
  +import * as fp from '../fp'
  class SeqDecoder {
  revsOn = false;
  @@ -123,12 +124,11 @@ class SeqDecoder {
  }
  cls() {
  - for (let y = 0; y < this.height; y++) {
  - this.c64Screen[y] = []
  - for (let x = 0; x < this.width; x++) {
  - this.c64Screen[y][x] = { code: 0x20, color: DEFAULT_BACKGROUND_COLOR };
  - }
  - }
  + this.c64Screen = fp.mkArray(this.height, () => {
  + return fp.mkArray(this.width, () => {
  + return { code: 0x40, color: DEFAULT_BACKGROUND_COLOR };
  + })
  + });
  }
  carriageReturn() {
  