helpers: enforcing py3k division in all templates

Shouldn't break anything.
helpers: added template_func()
core/operation: add_kernel() takes a renderable now
TODO: added a task
core/operation: removed cluda.kernel import
core/operation, helpers: added underscore to template def names to avoid intersection with user code
cluda/kernel: added deep ProcessedModule replacement
elementwise: using modules for the ``code`` parameter
Finished removing low-level render functions from core code