Syntax aware spell checking.

I want a spell checker that takes into account the mode's syntax, e.g., on Markdown I don't want it to spell check inside code blocks, on LaTeX I don't what it to check the macros, etc.

Of course, this would require information to be added to the syntax files saying what has to be checked or not, like Vim's `@spell`.

It does not need to take into account the browser's dictionary: a completely separate one could be used instead (possibly with word addition by user). This is not important to me now.

I notice that there is the `ext-spellcheck`, but I don't know what it does, and I haven't been able to get it to work.

1) Does it do what I want?
2) If yes, how to get it working?

If not, consider this a feature request for the syntax aware spell checking.

I have tried:
- `git clone`, then `./static.py`, then http://localhost:8888/kitchen-sink.html. It seems that spellcheck is enabled on the kitchen sink [at this line](https://github.com/ajaxorg/ace/blob/37aa4851379955269c398e26c6bcc4c37bee6d68/demo/kitchen-sink/demo.js#L38) , but I see nothing on modes like Markdown or Text. Do I need to do something else?
- a minimal test case from the build. `npm install`, `node ./Makefile.dryice.js`, then take `build/src`, and use the following file:

``` html

ACE in Action

#editor {
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
}

var editor = ace.edit('editor');
editor.setOption('spellcheck', true);

```

Are those methods working for anyone? Can anyone provide a minimal test case that works?

Related issues:
- https://github.com/zedapp/zed/issues/67. Mentions Stackedit, which does what I want but only for Markdown.
- https://groups.google.com/forum/#!topic/ace-discuss/-dwNC_rX7R0 and https://groups.google.com/forum/#!topic/ace-discuss/eRpKMgDdjx0, which ask about spell checking, but don't mention syntax awareness specifically.