Write-through caching in VFS

[LPGhatguy]

Rojo's "strategy" for two-way sync caching is currently write-around. This means we can't distinguish changes that come from Rojo editing files and changes from other processes.

If we write-through instead, we can ignore filesystem changes that occur from ourselves because the read-back file contents will be the same.

[LPGhatguy]

Taking a try at this by breaking away the VFS implementation into a separate crate in the vfs-crate branch.

[Boegie19]

I will take a shot at this as soon as #616 gets accepted or denied since else I will create a merge conflict as soon as it gets accepted