Accessibility and usability update

Thanks to some new contributions by Sean S. LeBlanc, EZM Reader has some improvements for accessibility and usability if hosted directly. The biggest changes are:

1. There is now an ALT option in ezmreader.js that allows you to add a description or a plaintext copy of your zine so it can be read by screen readers.

2. If you are hosting your zine directly instead of embedding it, metadata has been added to index.html so you have more control over what the preview will look like when your zine is linked on social media.

These improvements are possible because the EZM Reader is fully open source and available on GitHub. Feel free to contribute to the project if you have ideas of your own.