expand definition of data table to include index definitions from 'AdjustCounts'

[eosnas]

in the documentation for the historic data tables, expand the definitions of the various metric so that a user can fully understand the metrics without refoer to other pages of documentation. Specifically, include the following:

itotal - Indicated total. Singles doubled, pairs doubled, opens added, flkdrake 1-4 doubled, flkdrake 5+ added.
ibb - Indicated breeding birds. Singles doubled, pairs doubled, opens removed, flkdrake 1-4 doubled, flkdrake 5+ removed.
total - Total birds. Singles added, pairs doubled, opens added, flkdrake added.
sing1pair2 - Singles and pairs. Singles added, pairs doubled, opens removed, flkdrake removed.
flock - Flocks. Singles removed, pairs removed, opens added, flkdrake added

Also, include any variations from other "standard" waterfowl index calculations. For example, "indicated breeding bird" index for scaup, if these vary from the NAWBPHS or other FWS surveys.