change the way foreach_row works

also involved changing around the way _columns and _headers work
now using Class::PseudoHash
	this is suboptimal though
	need to invent Class::DataRow or somesuch
added prereq to myperl
Merge branch 'master' of github.com:barefootcoder/common
added Google::Worksheet->get_row

returns a pseudohash for the requested row
can give it a number or a key name
refactored pseudohash row building (also used in foreach_row) into a private method