fix "necessarilly" typo
fixed typos found by topy in all Markdown files

Topy is available at https://github.com/intgr/topy.
Updated website documentation for graceful_halt_timeout

The default value in the code is actually 60 seconds, so now the docs match that.
Removed unused halt timeout and check interval settings.
Merge pull request #3598 from mitchellh/remove-halt-timeout-from-windows-guest

guests/windows: Removed unused halt timeout and check interval settings.
Merge pull request #3597 from mitchellh/update-website-docs-halt-timeout-default-value

website/docs: Updated website documentation for graceful_halt_timeout
Merge pull request #3595 from berendt/topy

website: fixed typos found by topy in all Markdown files
Merge pull request #3594 from aspiers/provider-config-doc-typo

website/docs: fix "necessarilly" typo