Add Pattern method to Mux

[jirenius]

It should be possible to get the Path used when creating the Mux.

mux := NewMux("this.path")
mux.Path() // Returns "this.path"

Additionally, when mounting the Mux, there should be a FullPath that returns the path including that of the parent and the mount path.

mux := NewMux("this.path")
sub := NewMux("")
mux.Mount("sub", sub)
sub.FullPath() // Returns "this.path.sub"

[jirenius]

Resolved in #44