Add support for `proxy` and `without-ssl`

Most private object storage solutions support direct and proxy
configurations. For clients interacting with object stores in a direct
configuration, overriding `endpoint` works. In order to support object
stores in a proxy configuration, this commit adds a `proxy` option
(along with a `without-ssl` flag for interacting with object stores
without HTTPS).
Revert "Add support for `proxy` and `without-ssl`"

This reverts commit 91a03f6d2f0c82c0edc00e7d1f13e4ac2efc275a.
Add support for HTTP_PROXY and without-ssl flag

Most private object storage solutions support direct and proxy
configurations. For clients interacting with object stores in a direct
configuration, overriding `endpoint` works. In order to support object
stores in a proxy configuration, this commit adds support for the
`HTTP_PROXY` environmental variable (along with a `without-ssl` flag for
interacting with object stores without HTTPS).
Merge pull request #17 from hectcastro/hc-proxy-support

Add support for HTTP_PROXY and without-ssl flag