website/docs: make mention of docker provider on provisioner page
website/docs: document SSL share [GH-3672]
providers/docker: forward ports properly
kernel/v2: convert network type to symbol earlier
provisioners/shell: Fix shell provisioning when config.binary is set to false [GH-3712]

The `config` in use was the Shell provisioner config that does not expose
access to the VM configs.

References https://github.com/fgrehm/vagrant-lxc/issues/284
kernel/v2: automatically forward winrm if comm is winrm [GH-3685]
synced_folders/nfs: allow disabling export [GH-3636]
kernel/v2: multiple synced folder lines override each other
providers/docker: ability to specify build dir synced folder opts [GH-3727]