Previously we only supported HTTP_PROXY because the proxy support in Go
was lacking in older versions. Now that there is
`golang.org/x/net/http/httpproxy`, we can rely on that instead to gain
consistent support for HTTPS_PROXY and NO_PROXY.

Done by `dep init`

We might bring back the self-updater at some point, but right now it's
dead code and it's not clear to me how to implement it in a fashion
where it also updates dependent files such as shell completion scripts
and man pages.

After the last howeyc/gopass update, hitting Enter after password input
makes the next printed line appear indented to the position of the
password prompt. I'm not sure what causes this, but as a workaround,
skip the howeyc/gopass dependency altogether and interface directly with
crypto/ssh/terminal.

Fixes #1262

See https://groups.google.com/forum/#!topic/golang-nuts/kTVAbtee9UA

Also add `--browse` functionality to `create` and `release` for parity
with `issue` and `pull-request`.

howeyc/gopass@e7699d3d9eedadb8fafead56654e6459b57fe4cd

Fixes #1125, closes #1126

Sometimes when hub is cross-compiled, `user.Current()` won't work on
certain systems. Use an alternative way of obtaining the user's home
directory.