add utf8 support
add workaround for #1143 - utf8 egg not exporting byte-string-length
remove calls to make-slice
copy source string when doing string->slice
Revert "remove calls to make-slice"

This reverts commit 95bf8e43168fbe67da5c154d501bf33629ffba25.
clean up copied string data after converting string->slice
eliminate string->slice
update README to reference level egg
release 2.0.0