Fixed typographical errors pointed out by Bill Cleveland.

Added <fileVersion> element to <fileHeader> element, so each version of a particular DAVEfunc model can be uniquely identified. Format of the version identifier is undefined.

Added an email attribute to the <author> element. The eXtensible Name Service (xns) standard doesn't appear to be catching on as rapidly as hoped, so a static e-mail link will have to do for now, at least until the replacement XRI technology is more widely adopted.

Added a mandatory varID attribute to both <independentVarPts> and <dependentVarPts> so these can be associated with an input and output signal name (<variableDef>), respectively.

Added an optional <extraDocRef> element to the <modificationRecord> element so more than one document can be associated with each modification event; if only one document needs to be referenced, use of the optional refID in the <modificationRecord> itself will suffice.