CharVectorSlice missing from basis library

[ellerh]

There doesn't seem to be any CharVectorSlice in MLWorks, but it's required by the "standard":
http://sml-family.org/Basis/mono-vector-slice.html#CharVectorSlice:STR:SPEC

[NickBarnes]

The SML Basis Library was finalised some time after development of MLWorks stopped. There may be quite a few defects along these lines. Thank you for putting in the effort to find them.