Adds support and tests for elements from the podcast namespace...

[andrlik]

... as specified by the podcast index.

Specifically adds support at channel level for:

• funding url
• locked boolean

And at the item level:

• chapters url for json description
• podcast person elements
• transcript url

[andrlik]

All requested changes implemented in latest commit.

[thp]

Merged, thanks!

[thp]

Released in version 0.6.10.