Update CHANGELOG for new release
Update CHANGELOG for new release

Some minor development/documentation changes. Should be functionally the
same as 0.19.0, but since there are code changes, bump a version.

discoposse/vagrant-vsphere,vijayviji/vagrant-vsphere,edmcman/vagrant-vsphere,EdHurtig/vagrant-vsphere,higebu/vagrant-vsphere,lilirui/vagrant-vsphere,barklyprotects/vagrant-vsphere,mkuzmin/vagrant-vsphere