pip install couchbase attempts to build binaries

`pip install couchbase` attempts to build the binaries instead of fetching pre-built binaries.

This is because pip on Windows does not automatically pull down 'exe/msi/zip' binary installers.

Building couchbase locally happens as a fallback but then fails due to dependencies not being available (libcouchbase, libevent, etc).

We should find a way if possible to ship Windows binaries via PIP.