A simple renderer implementation. It's supposed to be as simple as
possible, thus easy to understand at the source level, and to use as few memory
as possible. Should be used when memory is a constraint and/or when the
rendering is stateless (that is, the application is not an interactive
viewer that displays the same map more than once). In the latter case, a
renderer that uses more memory but avoids recomputing map rendering details
is to be preferred.