Fix code example qualifiers (#373)

* Update spec.lock, 3 guidelines related but not affected
1) The two div-by-zero guidelines are related to https://rust-lang.github.io/fls/expressions.html#fls_Q9dhNiICGIfr
This element of the FLS hasn't significantly changed (dividing by 0 still results in panic).
2) One very old pointer guideline is related to https://rust-lang.github.io/fls/expressions.html#fls_9wgldua1u8yt
This element, as far as I can tell, hasn't changed significantly either (dereferencing dangling or unaligned pointers has been UB for a while).

* Fixed some rustdoc directives

* Tentative fix for wrong panic handling in playground runner

* Fixed more rustdoc directives

Author: felix91gr