begin rewriting Import
add mathics/autoload/format/Text/Import.m
Implement Conditional and Post Importers for RegisterImport
cleanup of RegisterImport
cleanup Import
implement conditionals for Import
Post importers are actually optional and occur seperately to defalt/conditional importers
cleanup Import tests
Implement Text Importer
fix bug in ReadList: graceful fail
implement StringSplit
implement CSV importer
add CSV to FileFormat
add example CSV datafile
update RegisterImport tests
make Read check if stream is open
cleanup of ReadList docs
implement ReadList[stream, types n] form
fix mistakes in RegisterImport tests
cleanup Import tests