Fix Issue 3, better vimdoc

* Removed tags file & added to the gitignore.
* Rewrote vimdoc to conform with help formatting.
* Added appropriate tags.

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I tried to also fix some grammar/English as I reformatted. I tried to minimize a bit of redundancy in re-explaining the toggles and just focused on non-obvious stuff.

**Code Note**
Here you've used g:foldfast_togglehook, g:foldfast_map & g:foldfast_mapsuffixes. It might confuse people since mapsuffixes actually modifies togglehook but appears to be related to map due to namespace similarity. In future, you might want to be careful regarding naming. I've tried to clarify this in vimdoc.

As this is part of your public API already published, modifying this isn't probably wise as it is already in some people's configs. Just a note for future dev.

On a more positive note, have fun with vim plugin dev and thanks for the plugin :)