Castero

**Added**
* Added the `e` key to execute a system command on an episode. Command can
be configured with the `execute_command` option.
* Added volume control keybinds.
* Added config options to use a proxy.

**Changed**
* Made the help menu scrollable.
* Made separate keybinds for saving/deleting episodes for offline
playback (`s` and `x` by default). Existing configs will be migrated.

**Fixed**
* Fixed an issue where feeds would, on some systems, not be displayed in order.
* Fixed poor UI performance when reloading feeds.
* Fixed time/duration display not being properly justified - Thanks buck10!
* Fixed an issue importing a certain structure of OPML subscriptions.
* Fixed an issue with episode IDs being reset when feeds are reloaded.

**Added**
* Made database operations multi-threaded to improve performance, especially
for users with many feeds.
* Added the `u` key for displaying an episode URL in the status bar - Thanks
jose1711!
* Added a perspective to display downloaded episodes. Press `4` to access it.

**Changed**
* Reduced the default input timeout, which is tied to the display refresh rate.
This will somewhat increase standby CPU usage. Users with low-end systems may
wish to increase this timeout with the `refresh_delay` config setting.
* Improved reporting of errors when importing OPML files - Thanks hebecked!
* Improved the overall UX of importing OPML files, with "live" database changes
and status reports.
* Changed the file naming format for downloaded episodes. Episodes downloaded
in earlier versions of castero will not be detected and must be re-downloaded.

**Fixed**
* Fixed stderr file descriptor not being found on macOS, causing a crash.
* Fixed the reloading status message to properly show the current feed number.

**Added**
* Added support for filtering menus with the `/` key.
* Added individual config options for foreground text colors.
* Added an option for default playback speed.
* Added the number of unplayed episodes to the menu header.

**Fixed**
* Fixed support for OPML v2.
* Fixed menu headers using the wrong background color.
* Fixed the metadata window not properly filling the screen height.
* Fixed the selected menu index being offscreen when resizing the window.
* Fixed menu selections not being sanitized in the correct sequence.
* Fixed menus not visually updating when modified.
* Fixed ffmpeg output appearing in the client - Thanks rien333 and jaseg!
* Fixed a crash when resizing the window at some ratios.
* Fixed a crash when trying to invert menus.
* Fixed a crash when an episode had no audio enclosure.
* Fixed a crash when episode enclosure caused a request exception.
* Fixed a crash when trying to play the current episode in the queue.

**Added**
* Added support for importing/exporting subscriptions to and from OPML files.
Many other clients support this format, so you are now able to easily move your
feeds between clients. To use this feature, run castero with the
`--import` or `--export` flag (or run `castero -h` for more info).
* Added support for preserving the queue when restarting the client.
* Added support for 256 colors - Thanks arza-zara!
* Added controls for playback speed - **[** and **]** by default.

**Fixed**
* Fixed a crash when viewing metadata for a feed with no description.
* Fixed custom_download_dir config option not being an absolute path.
* Improved scroll performance of episode menu with many episodes.
* Fixed a crash when vertically shrinking the client.

**Added**
* Added the name of the feed to episodes in the queue menu/perspective.

**Fixed**
* Fixed client not adhering to the max_episodes config option when reloading.
* Fixed the queue not progressing automatically on episode completion.
* Fixed a Python 3.5 compatibility issue.

**Added**
* Added download status "\[D\]" metadata tag to episode menu.

**Fixed**
* Fixed a crash when queueing a large number of episodes with the VLC player.
* Fixed delay when skipping ahead in queue.
* Fixed a crash when running with Python 3.5.
* Fixed crash when trying to create database file in nonexistant directory.
* Fixed episode menu not updating on feed delete.
* Fixed menus not updating when terminal dimensions change.
* Fixed user metadata (i.e. played status) being overwritten when reloading.