Fix go version in docs

The current link 404's, but this fixes it.

Thanks to copyedt on Twitter: https://twitter.com/copyedt/status/620807196259958785

Fix interpolation in google compute image name

Use Rack::Protection

Fix other characters in docs displayed incorrectly

Fix character being displayed incorrectly in hashicorp ecosystem page

builder/null: When using a Null builder, this error message is incorrect.

Remove ssh_wait_timeout from doc basic examples for virtualbox/vmware…

The default image name in the code has a bug. It is being set to packer-{{timestamp}}, the {{timestamp}} part needs to be interpolated. Without the interpolation the GCE builder fails with
the following error

==> googlecompute: Creating image...
==> googlecompute: Error waiting for image: googleapi: Error 400: Invalid value for field 'resource.name': 'packer-{{timestamp}}'. Must be a match of regex '(?:[a-z](?:[-a-z0-9]{0,61}[a-z0-9])?)', invalid

Add 'edit these docs' link in the website footer

Wrap SSH handshake in a timeout

Fix #2830.

wesbtei: Fix NULL builder config documentation.

Change from "host" to "ssh_host" was introduced in d545431f