Make sure that the `struct` argument of `sp-get` is only evaluated once
Make arguments of `sp--next-thing-selection` optional
[Issue #158] Fix killing of blank lines.
Make `sp-transpose-hybrid-sexp` take num. argument to call `transpose-lines` instead. Advance the point to the line after the H-S. When selecting next H-S, start at next sexp, ignoring whitespace.
[Issue #158] Make "smart" behaviour of `sp-kill-hybrid-sexp` customizable (off by default).