V2.0 RC 3

This is the third release candidate for libbgpstream version 2.0.

Changes since rc2:

• Fixed bgpstream_pfx_set structure v4 v6 reference bug
  • This also reduces memory consumption for v4 prefixes in the set
  • Added tests for bgpstream_pfx_set
  • Updated API docs for bgpstream_utils_pfx_set
• Parser warnings is now disabled by default
  • Use --enable-parser-warnings flag during configure to show the warnings
• Minor clarification on the bgpreader help text
  • Thanks @cmosig for the pull request