Move FS Node implementations from server/ram_fs to include/ram_fs.
Support embedded ram_fs instances in VFS configurations using <ram/>.
Add 'no space' handling to VFS symlink ops.
Fixes#1635
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082