Update taskrc VIM syntax file for 2.4.0
Update taskedit.vim for multiline values

Commit 0c1fa8b enables multiline value for "Description:". Update
taskedit.vim syntax file for this:

  1) Now all keys are required to be indented exactly 2 spaces.
  2) We treat all keys equally, allowing all values to span multiple
lines, up until the next key.
taskdata.vim fixes; ftdetect backlog.data as JSON