message: Implement the 'hidden' char attribute
diff: * Copyright 2019 Simon Edwards <simon@simonzone.com>
  */
  -import { CharCellGrid, FLAG_MASK_WIDTH, FLAG_WIDTH_SHIFT, FLAG_MASK_EXTRA_FONT, STYLE_MASK_CURSOR } from "extraterm-char-cell-grid";
  +import { CharCellGrid, FLAG_MASK_WIDTH, FLAG_WIDTH_SHIFT, FLAG_MASK_EXTRA_FONT, STYLE_MASK_CURSOR, STYLE_MASK_INVISIBLE } from "extraterm-char-cell-grid";
  import { log, Logger, getLogger } from "extraterm-logging";
  import { ColorPatchCanvas } from "./ColorPatchCanvas";
  import { FontAtlas } from "./FontAtlas";
  @@ -484,7 +484,8 @@ export class CharRenderCanvas implements Disposable {
  renderedCharWidthCounter = Math.max(renderedCharWidthCounter,
  ((renderedFlags & FLAG_MASK_WIDTH) >> FLAG_WIDTH_SHIFT)+1);
  if (mustRender) {
  - this._fontAtlas.drawCodePoint(ctx, codePoint, style, i * cellWidth, j * cellHeight);
  + const effectiveCodePoint = (style & STYLE_MASK_INVISIBLE) ? spaceCodePoint : codePoint;
  + this._fontAtlas.drawCodePoint(ctx, effectiveCodePoint, style, i * cellWidth, j * cellHeight);
  }
  }
  