Reset link input value on highlight

When a user creates a link and then goes to create another, the url from the first link is displayed as the default value in the input for the second link. This commit causes the link input value to be reset so when the user goes to create a second link they will have a blank input.
Merge pull request #97 from chasingmaxwell/patch-1

Reset link input value on highlight
Avoid positioning the menu outside of the window
added comment
Updated to pass jshint test
Updated to use insertRule and deleteRule instead of addRule for compatibility reasons
Merge pull request #98 from mattmontgomery/avoid-document-overflow

Avoid document overflow :) thx @mattmontgomery