Issue 13647: improve std.traits navigation table.

Give more meaningful name to 'xxx' category!
Sort identifiers in each category so that they're easier to find!
Improve awkward sentence.
BigInt @safe

some more

some more

some cleanup

some more

hope I got them all

another one

another one

some more

review fix and some additional style changes

some more quickfur
Fix issue 13594: next(Even)Permutation doesn't need to take input range by ref.
Merge pull request #2651 from quickfur/issue13594b

Fix issue 13594: next(Even)Permutation doesn't need to take input range by ref.
Merge pull request #2649 from quickfur/issue13647

Fix issue 13647: improve std.traits navigation table
Merge pull request #2612 from burner/bigint_safe_one

BigInt @safe https://issues.dlang.org/show_bug.cgi?id=13607