converters/bibtexconv: Update to 1.1.11 [1]

Update MASTER_SITES and WWW. [1]
Improve LICENSE.
Switch to options helper (EXAMPLES).
Include script ietf2bibtex (Python 3 dependency) and USES=ssl.

PR: 223328
Submitted by: dreibh@iem.uni-due.de (maintainer) [1]