This commits changes class name of MarkdownListPreprocessor to
MarkdownListPreprocessor. It also changes corresponding references
in tests.
This is part of series of commits which aims for renaming bugdown to
markdown.
This commit is first of few commita which aim to change all the
bugdown references to markdown. This commits rename the files,
file path mentions and change the imports.
Variables and other references to bugdown will be renamed in susequent
commits.