Fixed bugs with mobile nav and added navbar toggling feature

There were problems with the menu on Android where it wasn't able to be clicked once the user scrolled, so I resolved that by altering the markup. I also reduced the clickable area of list items to prevent accidental navigation to the About page when trying to close the nav menu.

I added a feature for iOS which hides the navbar when the user scrolls down. This is a very common feature on apps like Pinterest and Google+.

I also added a selected color to the nav button which is the same as the hover state of social media icons on desktop.