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.
Merge pull request #3 from reidmv/verify_peer

Add support for unverified SSL connections