removes useless PageEntryMeta class; minor rest api changes

- `PageEntryMeta` is not needed, thus removed
- use `complete` parameter instead of `meta` for retrieving
  a single entry (same as used when getting the list)
- remove endpoint that returns a tag list of an entry; this
  is already covered when getting meta data for an entry
- remove possibility to get an entry via url parameter in
  favor for the path endpoint is supported
- fixes and improve documentation (README)
- changes date format in index (yyyymmmdd instead of
  yyyy/mm/dd)
- ignore negative values for `size` and `num`