gitignore: ignore eric4 project files
refactoring
- changed some variable names to be more self-explanatory
- episodes
 - generate their own destination path now
 - get learn their podcast's name now
 - root download dir only passed at download time and not part of episode information
  - should make it possible to relocate the root dir without having to recreate all feeds
- feeds
 - only generate basename of episode file, not full path (see above)
 - removed the %podcastname% modifier as it was used to build a path
  - this is now automatically done by the episode class (see above)