Had a play at making the following changes today, some will be a bit ugly as just...

- amend sql and add extension control file
- add in a basic replace function
- replace value comparison logic and handle nulls - this is still lacking
- move some duplicate logic out, but lots left
- have a go at putting together jsonb_replace_path and jsonb_delete_path functions, these are very rough and can be done better with proper thought.