Update frontiers-medical-journals.csl

Added Year to bibliographic entries for type Book (and many other types).  Removed "and" before last author or editor.

Concerning periods following author initials: note that real, published articles violate the official spec; author initials are specified by example as having trailing periods, but real articles published in these journals omit those periods.  This commit follows the official spec; I believe I should contact the editors, have them update their spec to match actual practice, and then update frontiers-medical-journals.csl, and maybe frontiers.csl.
Merge pull request #888 from cforden/patch-2

Update frontiers-medical-journals.csl