Add syntax highlighting in README.rst
Add a 'memoized' decorator

The `memoized` decorator caches a function or method return value only
if the current Flask application is not in debug mode.
Memoize bundles processed contents

Contents generated by bundles are memoized (cached) to avoid unnecessary
calculations.
Memoize assets processed contents

Contents generated by assets are memoized (cached) to avoid unnecessary
calculations.
Add method docstrings