Ignore indented lines that aren't part of a test

[pjeby]

Currently, cram treats any indented line as though it were part of test output, even if it's not adjacent to a command, continuation, or other output line. This PR makes it ignore lines that are not part of a test or its output, even if they are at the same indent level.

[pjeby]

Please note that the build failure here is caused by the pep8 deprecation warning; with the changes in #30, this code actually passes the tests. (And of course it adds a regression test for the change.)

[roman-neuhauser]

This is implemented in Dram (https://git.sr.ht/~rne/dram).