sentinel slicing improvements

* add runtime safety for slicing pointers, arrays, and slices.
 * slicing without a sentinel value results in non-sentineled slice
 * improved `std.debug.panic` handling of panic-during-panic
8918cb06fcAndrew Kelley committed on 12/20/2019, 11:28:59 PMparent26f3c2d
6 files changedLine totals unavailable