libc manpages: various improvements from NetBSD

• Add STANDARDS and HISTORY sections within the appropriate manpages
• Mention two USENIX papers within kqueue(2) and strlcpy(3)

Reviewed by: bcr (mentor)
Approved by: bcr (mentor)
Obtained from: NetBSD
MFC after: 7 days
Differential Revision: https://reviews.freebsd.org/D24650