Added basic module logic and a test for it
helpers: template_from() can now take templates too (which are just returned unchanged)
cluda: reworked template creation and processing

As a result, changes in ocl.py were rolled back - now submodules are passed
among normal render keywords.
cluda/kernel: removed render_template_source()
doc/history: added a note about module support and a tutorial stub
Merge branch 'feature/modules' into develop