Add option to not raise footnote markers etc.

[blaenk]

The raised footnotes look pretty weird to me, they do look better with markup hidden but I'd rather not do that, so I was looking into simply disabling it on my end but it didn't seem immediately obvious to me how to accomplish that.

[blaenk]

It seems like it's just a matter of doing:

(defconst markdown-inline-footnote-properties nil)

I'll close this after getting some confirmation.

[jrblevin]

I think that should work for now, but it would be better for users I think if there was a defcustom for this (something I plan to add).

Coincidentally, @saf-dmitry also mentioned this as a comment to #130, so perhaps we should move any future discussion here.

[blaenk]

Sure thing.

[jrblevin]

I mean let's leave this one open since the other one is a broader, already closed issue. :)

[jrblevin]

Footnotes are now only raised when markup hiding is enabled, and the display properties (raise amount, scaling) can now be customized via markdown-footnote-display. Sound good?

[blaenk]

Yeah that sounds reasonable.