TODO

TODO

- Better error handling: current situation is not very nice on the user. This
  probably results in writing own expression parser that understands variables
  and commands on its own. No more ugly regex-substitutions.
- Caching the results or similar performant functionality. Re-evaling the whole
  file on every single small change can be taxing. Could we store cache on temp
  files to keep this standalone. Vim-Python sure would be another option, but I
  don't really like the sound of it. 
- IDEA: sums wouldn't accumulate by default, but prefix with + to acc.
- IDEA: export CSV in some meaningful manner?

NOT GONNA DO (rendered pointless)

- column sum to answer some issues:
    - when collecting numbers save the column #
    - @csum will sum up those numbers in the right column.