refs #18: flake8
refs #18: added a test showing the incorrect behaviour
refs #18: dealt with mangled ilvl in lists
refs #18: update note
refs #18: refactor
refs #18: updated the test for no longer doing stupid nesting
refs #18: break ``get_li_nodes`` early if it detects a mangled list
refs #18: updated update note
Merge pull request #18 from PolicyStat/issue_18

Deal with invalid list id/indent level combinations.