std.digest: Publicly import LetterCase
Make std.utf.toUTFz safe and pure
Merge pull request #2023 from tom-tan/safe-pure-std-utf-toUTFz

Make std.utf.toUTFz safe and pure
Mark std.stdio.fopen and popen as trusted
Merge pull request #2022 from CyberShadow/std-digest-public-import

std.digest: Publicly import LetterCase
Merge pull request #2026 from tom-tan/trusted-std-stdio-fopen

Mark std.stdio.fopen and popen as trusted
Mark std.stdio.File.this, opAssign, open and popen as safe
Merge pull request #2027 from tom-tan/safe-std-stdio-File-this

Mark std.stdio.File.this, opAssign, open and popen as safe