Revert to PNG for build status image

The text in SVG for build status image appears larger than the
text in PNG for coverage image, so revert to using PNG for build
status image which has a text of size that matches the size of
the text in coverage image.
Improve coverage in test for form examples

In the test for form examples, the tests are not testing the
route that displays the form. The tests are only testing the
result of the form submission. As a result, not all code in the
tests is being executed. Ensure that 100% of the test code is
executed by testing the route that displays the form.
Add test for empty PATH_INFO in environ

There is a check in ice.Request that tests if the value for
PATH_INFO key in environ dictionary is an empty string. If it is
found to be an empty string, the value is set to '/'. This check
has not been tested in the tests for this class. As a result,
the ice module does not have 100% test coverage. Fix this by
adding a test for this check.