Identify misspelled words

[syntag]

Please add a way for SpellCheck to detect and automatically underline misspelled words similar to Word Doc. The reason why this is useful is half the time I don't even know if I misspelled a word and I think that would make this feature more handy.

[Pysis868]

Issue title could be updated to include that you want this done 'automatically' (as do I :) ) during normal editing with the document open.
I believe having this run automatically will certainly improve our flow better as being apparent, so we can't be expected to remember to run it every time we want the document checked.