org-caldav-cleanup-ics-description: properly clean ranged timestamps from description
org-caldav-sync-result-print-entries: insert "None" without entries
org-caldav-select-tags: add variable to sync only entries with specific tags
org-caldav-inbox: enable specifying a heading, where to add new entries

enables org-capture like syntax for specifying a heading, under which
new entries will be filed.

- "path/to/file"
- (file "path/to/file")
- (file+headline "path/to/file" "heading title")
- (id "<uid>")
org-caldav-calendars: support multiple calendars

if defined, this variable will be iterated over and selectively
overwrites the default configuration.