libcaca v0.99.beta20

• IPv6 support in cacaserver
• fixed a bug from 2004 that caused PDF documentation generation to fail
• memory allocation functions are now more robust
• numerous fixes for memory leaks and invalid memory accesses:
  • CVE-2021-30498
  • CVE-2021-30499
  • CVE-2021-3410
  • CVE-2018-20546
  • CVE-2018-20547
  • CVE-2018-20545
  • CVE-2018-20548
  • CVE-2018-20549