Devised scheme for layering documents onto k-v logbase.  Uses numerical
"MCID" or Master Catalog ID as a record ID to speed up map lookups,
		which a quick test showed is about twice as fast as string key
		lookup.  Documents will be stored in a value as a map between
		string labels and MCIDs or other values (i.e. fields).
	  	Permits efficient linking between documents which is crucial.
		Document "kinds" (types) will be able to store schema using this
		field map.  The use of MCIDs takes advantage of a feature of Go
		maps whereby you actually get many maps within a map using
		interface{} keys.  All of this benefits from the logging nature
		of the logbase, so everything is easily altered.  However, the
		price is that to retrieve a document, we may need to retrieve up
		to the number of fields from separate k-v pairs.  This is
		mitigated by the ability to embed values in the document.  But
		the first step is to change a MasterCatalogRecord into an
		interface allowing the MasterCatalog map to include not just
		(fnum,vpos,vsz) triplets but also mcid values.  Done, with
		current tests passing.