`render_model` now works just like `include` and can take `with` and `only` arguments
Fail better. This change mirrors `django.template.loader_tags.IncludeNode`. I didn't include it in the previous commit to show test consistency.
Tests for render_model with/only.

Using similar scenarios as Django uses to test `include` in `tests.regressiontests.templates.tests`.
Readme updates

- add render_model with/only documentation
- add a cheat sheet of all template tags
- add documentation of render_list and render_iter
Merge branch 'render_model_with' (pull request #15) into v1.3.0-prep

* render_model_with:
  Readme updates
  Tests for render_model with/only.
  Fail better. This change mirrors `django.template.loader_tags.IncludeNode`. I didn't include it in the previous commit to show test consistency.
  `render_model` now works just like `include` and can take `with` and `only` arguments

Conflicts:
	armstrong/core/arm_layout/templatetags/layout_helpers.py
	armstrong/core/arm_layout/tests/templatetags/layout_helpers.py