* #23 - support for sorting by metadata
- added support for grouping items by the presence of specified metadata
- new keyword `with-metadata:` introduced for that purpose in lexer
- if metadata field name is omitted, the default `sort-index-value` is used
- added support for sorting items by notes and folders metadata
- new keyword 'by-metadata:' introduced for that purpose
- if metadata field name is omitted, the default `sort-index-value` is used (or metadata name inheritance is used)
- unit tests of sorting spec processor extended accordingly
- documentation and code example in README.md
- extended to also support true alphabetical on metadata fields
- release unnecessary references after sorting completed
SebastianMC
SebastianMC