[FIX] Replace all non-breaking spaces with vanilla spaces

[nicholst]

This PR replaces all non-breaking spaces with spaces (or deletes them if they were adjacent to a space).

As far as I could tell, none of these non-breaking spaces occurred with purpose, but were rather accidental. (Only purpose I can think of is to avoid a number getting separated from a unit, but they have not been used in this way so far in the BIDS spec.)

I realise it doesn't really matter, but my editor highlights them and, in the spirit of keeping clean and simple ascii markdown, I thought they should go.

(For reference these were found with grep $'\xc2\xa0' *.md)

[sappelhoff]

Cool, I didn't even know there were characters like that. +1 to get rid of them - thanks!

You accidentally misaligned one table pipe, that's why Travis CI is complaining. I made a suggestion to fix it.