README.third_party.md includes a list of third party dependencies, their current version as vendored into the codebase, and their upstream's most recent known version. These libraries are included in a Markdown table, so this information is clearly visible in Github. The names of the libraries in the leftmost column are links to the sources for upstream version information. This allows us to easily audit for new releases we should consider for vendoring.

peglib is missing a link which can be inspected for identifying new upstream versions.