chore(release): 1.0.0-alpha.20 [skip ci]

# [1.0.0-alpha.20](https://code.podlibre.org/podlibre/castopod/compare/v1.0.0-alpha.19...v1.0.0-alpha.20) (2020-11-24)

### Bug Fixes

* **import:** use <image><url> tag when no <itunes:image> is present ([20e607af](https://code.podlibre.org/podlibre/castopod/commit/20e607afb755bc75056041738fa7cbf6723d754c))

### Features

* **rss:** add podcast-namespace tags for platforms + previousUrl tag ([dbba8dc5](https://code.podlibre.org/podlibre/castopod/commit/dbba8dc58133967c778514268cbfed8098ed1dbc)), closes [#73](https://code.podlibre.org/podlibre/castopod/issues/73) [#75](https://code.podlibre.org/podlibre/castopod/issues/75) [#76](https://code.podlibre.org/podlibre/castopod/issues/76) [#80](https://code.podlibre.org/podlibre/castopod/issues/80)