nomcompile3: Build a set of nomenclature files

An instance of this subclass of AbBind represents a code that is a direct equivalent of another code. Here is the interface:

# - - - - -   c l a s s   E q B i n d

class EqBind(AbBind):
    '''Represents a direct equivalent code.

      Exports:
        EqBind ( abbr, prefSym, engName ):
          [ (abbr is a stripped, uppercased bird code) and
            (prefSym is the AbSym instance for the preferred code) and
            (engName is the English name on which this code is based) ->
              return a new EqBind instance representing that binding ]
        .abbr:        [ as passed to constructor, read-only ]
        .prefSym:     [ as passed to constructor, read-only ]
        .engName:     [ as passed to constructor, read-only ]
    '''