Make Print Functions Consistent with --keep-empty-lines

[CauhxMilloy]

• Updating batslib_count_lines to automatically detect trailing newlines and count them if present.
  • This works on the concept that a string has a trailing newline if it was intended -- e.g. via run --keep-empty-lines or similar.
• Updating batslib_prefix and batslib_mark to accept --keep-empty-lines option to properly print empty lines and trailing newlines.
• Updating batslib_print_kv_single_or_multi calls to batslib_prefix.
  • Will automatically detect trailing new lines (on a per-value basis).
  • If trailing newline is present, --keep-empty-lines will be passed to batslib_prefix.

This implements option 4 for batslib_count_lines and batslib_print_kv_single_or_multi, and option 2 for batslib_prefix and batslib_mark, as discussed in #11.

Fixes #11.