DownloadUnzip downloads and unzips client libraries.

DownloadUnzipIfMissing downloads libraries `libs` into directory `dst` if the libraries don't already exist.

DownloadURL returns the URL of the client library archive for the given language and service name/version.

LandingPage returns the client library landing page for the given language and service name/version.

Lib represents a downloadable client library.

MemBuffer implements Buffer in-memory.

Buffer is the interface to provide DownloadUnzip with buffer space.