add initial sheet support in Reader
test branch commit
multiple filter reader and new series reader
incomplete code
fully passed old test code
optimal functional setup
upgrade Reader to include various filters
create multiple sheet support while keeping backward compatibility
mutliple sheets reader is mature
made refering to subsheets easier
default iterator is to iterate row by row
book iterator is done
satisfied all existing test cases
book reader and writer is close to finish
delete temp test file
update readme
write from reader
test cases for csv book writer and write a book reader
documentation update and more test cases
geting rid of useless filterable reader. confusing for end user