* #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
- added two new commands to enable/suspend the plugin
- intentionally put in the description convenient names: sort-on and sort-off
- code area was not covered by unit tests, not adding new one at this point (simple logic, fresh mind ;-)
- new syntax: target-folder: Reviews/* <-- applies to folder, subfolders and all descendant folders
- new syntax: target-folder: Reviews/... <-- applies to folder and subfolders
- special case: target-folder: /* tells the plugin to apply the specified sorting to entire vault
- enhanced syntax for '.' - can be used to specify relative path now (e.g. target-folder: ./daily)
- added new sorting attribute (sorting: standard) to actually give back the sorting into the hands of standard Obsidian mechanisms
- fixed a minor bug: some of error messages were displayed only in console, not in the ballons
- unit tests for all new and changed functionality
- pending README.md update