Make MD004 work only on ul, and clarify MD005 behavior
Make MD004 work only on ul, and clarify MD005 behavior

Fixes #40

MD005 description is changed to point out that it applies to both ordered and
unordered lists. MD004 will now only work on unordered lists.

Borgaard/markdownlint,DavidAnson/markdownlint-ruby,markdownlint/markdownlint,mivok/markdownlint,peter1000/markdownlint,exalted/markdownlint