v0.4.0

• Breaking: Rename TagInfo*Error classes to Taginfo*Error
• Breaking: Move the PrevalentValue class from api.v4.key to api.v4.key.prevalent_values
• More endpoints are implemented:
  • /api/4/key/chronology
  • /api/4/key/combinations
  • /api/4/key/distribution/ways
  • /api/4/key/projects
  • /api/4/key/stats
  • /api/4/relation/projects
  • /api/4/tag/projects