add inbounds to some more substrings

[KristofferC]

Before

julia> @btime rstrip("dsfsdfdsf ");
  114.895 ns (4 allocations: 80 bytes)

julia> @btime lstrip(" dsfsdfdsf");
  60.079 ns (2 allocations: 48 bytes)

julia> @btime chomp("fdsfd\n");
  46.178 ns (1 allocation: 32 bytes)

julia> @btime rsplit("aba, aba, aba", ',');
  364.071 ns (6 allocations: 256 bytes)

After

julia> @btime rstrip("dsfsdfdsf ");
  101.403 ns (4 allocations: 80 bytes)

julia> @btime lstrip(" dsfsdfdsf");
  46.380 ns (2 allocations: 48 bytes)

julia> @btime chomp("fdsfd\n");
  33.989 ns (1 allocation: 32 bytes)

julia> @btime rsplit("aba, aba, aba", ',');
  328.436 ns (6 allocations: 256 bytes)