fixed highlight bug & modified .gitignore

1. Line 21 : Because the different output which is complied by the 'marked' of new version, the header tags in .html have 'id' attribute. It makes the selector $('section [id]') contain more elements than before, so that the highlight navigation will be error.

2. Line 24: Make the highlight switching of the navigation more readable.

3. Line 36: When initial the webpage  scroll == 0, the if statement will never be true, so the articleID is always the last article's id, not the first.

pls fix these and deploy to the gh-pages. :)