Assert minimum bwrap version on host

Closes #271 (closed)

I added code checking the version of Bubblewrap and also updated the docs to reflect the specific version requirements.

Here's a table of what bwrap options we're using and when they were introduced:
--ro-bind 0.1.0
--uid 0.1.0
--gid 0.1.0
--unshare-pid 0.1.0
--bind 0.1.0
--unshare-net 0.1.0
--unshare-uts 0.1.0
--hostname 0.1.2
--unshare-ipc 0.1.0
--chdir 0.1.0
--proc 0.1.0
--tmpfs 0.1.0
--dev 0.1.0
--dev-bind 0.1.0
--remount-ro 0.1.2
--version 0.1.0