Nimscripter - Easy Nimscript-Nim interop

[cblake]

@ElegantBeef, I get 170 ms for that program. `--experimental:vmOpsDanger` made 
no difference to that (or to `nim e`). Doing a PGO build with the gcc C backend 
I got 155 ms, 1.10x faster. { I should have perhaps mentioned, `nim e` timing 
wise, that my nim is a gcc-10.2 compiled recent devel, but these numbers sound 
similar-ish to what @ElegantBeef was seeing. }