fix: don't write file if no output has been generated
dev: rename files in source directory to be easier to maintain

-   tweak user messages
test: updates test files and rename them
fix: update info to follow pandoc's example
dev: implement writer-specific tests
dev: improve test info display
fix: update runtest.py documentation
dev: make display of diffs more consise
fix: diff order
update todo list
update info messages
fix: don't change list when pretty printing it
implement blacklist for tests
fix: workaround for https://github.com/jgm/pandoc/issues/1732