Simplify the syntax of CREATE/ALTER TEXT SEARCH DICTIONARY by treating the

init options of the template as top-level options in the syntax.  This also
makes ALTER a bit easier to use, since options can be replaced individually.
I also made these statements verify that the tmplinit method will accept
the new settings before they get stored; in the original coding you didn't
find out about mistakes until the dictionary got invoked.

Under the hood, init methods now get options as a List of DefElem instead
of a raw text string --- that lets tsearch use existing options-pushing code
instead of duplicating functionality.