Add support for subcategories

[endkb]

Subcategories should look like this:

<itunes:category text="Comedy">
    <itunes:subcategory text="Satire"/>
    <itunes:subcategory text="Stand-Up"/>
</itunes:category>

https://podcasters.apple.com/support/1691-apple-podcasts-categories

[endkb]

Rewrote the routine that reads the category field from the profile. It still splits the values at commas and puts them into an array, but it also now reads each value in the array and looks for a greater than (>) sign and splits that into an array as well. From there, the first value becomes the category and everything following becomes a subcategory of that.

CATEGORY=Category 1>Subcategory 1.1>Subcategory 1.2,Category 2>Subcategory 2.1

Becomes

<itunes:category text="Category 1">
    <itunes:category text="Subcategory 1.1"/>
    <itunes:category text="Subcategory 1.2"/>
</itunes:category>
<itunes:category text="Category 2">
    <itunes:category text="Subcategory 2.1"/>
</itunes:category>