Mark a constructor of std.format.FormatSpec as @safe, pure
Mark std.string.lastIndoxOf as @safe pure
Merge pull request #1489 from tom-tan/safe-pure-string-lastIndexOf

Mark std.string.lastIndoxOf as @safe pure
Merge pull request #1578 from tom-tan/safe-pure-nothrow-this-format-FormatSpec

Mark a constructor of std.format.FormatSpec as @safe, pure, nothrow