textutils: show_diff() API clean-up
- Fixes the spelling mistake in 'sufix' parameter. (closes #1465)
- Makes the function more generic by removing the hard coded html tags.
- Adds tests to the textutils_unit_tests for show_diff() function.
- Fixes the usage of show_diff function in bibedit_engine, so it will work after changes in this function.
Signed-off-by: Sebastian Witowski <sebastian.witowski@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>