Abstraction for using virtual paths. That means, we are resolving paths like:
(:key:)/foo/bar to something like /beer/foo/bar (under the assertion that key=/beer)
A vpath-interface is a set of standardized keys. Setting an interface will copy its values to the keys table.
Name of Interfaces:
(keys are not prefixed for system global locations)
Lets think about interfaces for file endings of compiled things. like: os.exe_suffix os.lib_suffix