Add a default (present) to the ensure property

This allows the resource to be used without explicitly specifying
ensure. I expect that in 90% of use cases ensure=present is what is
intended, so this potentially saves a few characters or lines.
Merge pull request #4 from reidmv/default_ensure

Add a default (present) to the ensure property
Add support for unverified SSL connections

Sometimes it is required to download a file using SSL from a server
using a self-signed or otherwise unverifiable SSL certificate. This
commit introduces a new parameter, :verify_peer, which accepts a boolean
true/false argument which when set to true allows download from an
unverified peer.