Minimal EMMA XML report support.

Creates `coverage.xml` in the output directory; coverage by class
or method are not properly filled, forms translate as blocks and
lines are obvious.

For lines the percentage is calculated as covered vs. instrumented.

The total number of forms is mapped to `/report/stats/methods[value]`.
avoid division by zero
Use `data.xml` for proper xml generation.

Feels a lot cleaner :-)
Merge pull request #24 from undernorthernsky/master

Emma report format
Fully resolve head symbols during instrumentation

Thus not mistaking a namespace function called loop for clojure.core/loop
Rework instrumentation to respect local scope

This is done by delaying instrumentation until we can leverage the &env
macroexpansion variable for local scope.

Fixes #21