updated [select_single_exn] to fail on multiple matches, as promised by a comment in its interface.
added support for selection of keys containing spaces.
added a -drop flag to [sexp select] and [sexp multi-select] that will output the original sexp with the matching fields removed, rather than printing out the matches themselves.
Release v0.16.0
Added new function Sexp_select.select_staged, which is a staged version of Sexp_select.select that is more efficient in scenarios when evaluate the same select expression across multiple inputs.