Support newlines specific to Python's `str.splitlines()`

[jwodder]

Python's str.splitlines() method treats the following as newline sequences in addition to the normal Unicode newlines already recognized by this library:

• U+001C ("file separator")
• U+001D ("group separator")
• U+001E ("record separator")
  • Used by JSON Text Sequence (RFC 7464) to prefix each JSON item (suffixed by LF)

How widely are any of these used as any sort of newline sequence?