Yet another section on permance: etale ring maps

There is already such a section for completion and another for
henselizations. But you can never have too many of these it seems.
Regular local ring is etale local for morphisms of germs
Definition: algebraic space regular at a point
Closed point on decent space is closed subspace
Dominate modification of regular surface by blowups

First version
Add reference to Bokstedt-Neeman

Thanks to Benjamin Antieau
http://math.columbia.edu/~dejong/wordpress/?p=3717&cpage=1#comment-1123465
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