should optionally support using https://github.com/dmatora/vagrant-unison additional to default rsync

[hoatle]

for a truly 2 way sync

try this to see if rsync or unison is better.

[hoatle]

this will help a lot on Windows machine, and moreover, this will make sure we always have two-way sync for different providers (multi provider two-way sync support)

[hoatle]

I can foresee that we're going to use native hypervisor instead of virtualbox soon when the vagrant providers are mature enough.

for example:

• https://www.vagrantup.com/docs/hyperv/
• https://github.com/sirn/vagrant-xhyve
• https://github.com/vagrant-libvirt/vagrant-libvirt

and many other providers so that we can get high-performance VMs to work with.

[hoatle]

closed for now, using different providers could help on this.