Properly scoped and selected the import of std.traits in std.ascii, so that it is only imported for the 2 functions that use it, toLower and toUpper.

There are also a couple of style changes, namely the ordering of values in an anonymous enum, and the use of only 1 indent level within an array declaration. The final change is to mark toLower and toUpper explicitly as @safe pure nothrow, as these are checked in unittests, but a unittest wouldn't tell you what was causing one of the attributes to not be valid for them.