added back in template call to subscribe link
set global path for cdn, fixed typos
adding link to CC-BY licence
removed explicit reference to image, added explicit reference to episode number
added explicit link to podcast homepage using site variable
changed reference to image location to use yaml variable, and our understanding of the naming convention of where images are hosted.

fixed explicit links to podcast homepage and to episodes to use the url strucutre that we agreed on.

closes #14, fixes #14
Merge pull request #15 from elifesciences/check-links

Check links