guests/nixos: don't detect as Windows [GH-4302]
core: preserve downloaded file in more cases [GH-4301]
core: fix crash case with provisioners [GH-4281]
Clarify error message for VAGRANT_HOME [GH-4256]
providers/docker: single port works [GH-3991]
website/docs: document synced folders and networking [GH-4003]
core: Machine#reload
commands/rsync-auto: check machine ID prior to sync [GH-4031]