Wrap doc window at edge of frame

[HawkinsT]

Fixes #165. Can return to the old behaviour with company-box-doc-no-wrap, but this option can be removed if it's not wanted by anyone.

[sebastiencs]

Thanks @HawkinsT , merged in f957e05933ed7604a0f87b488303345b93187c42.

I made a small modification in c3a78e994431fb6de4d67d2364b6453b1e17903a to use the faster frame-native-{width,height}