Added Iterl, Iterr, and Popl support, renamed Pushf and Pushb to Pushl and Pushr.
Switch to use of Any everywhere.
Implement Headr and Tailr, with tests.
Add Sliceable to node interface, and convert to (node) in buildr rather than Sliceable directly, to make explicit that it must be a node2/3.
Merge pull request #5 from nshepperd/viewr

Viewr
Re-organise code into files based on structure/interface

Removes functions for folding/iterating over slices, as those are already implemented as methods on the Slice type
Use Slice in preference to []Any
Split tests into separate files
Add Headl and Taill
Improve fold* tests, implement Popr
Merge pull request #8 from alaroldai/popr

Improve fold* tests, implement Popr