* Does not try to forcefully cast column content to float
* Silences any errors during formula evaluation, you can look at
`v:errmsg` to see if there was any error during the evaluation for
debugging
- Min: get the lowest value
- Max: get the highest value
- CountE: count the number of empty cells
- CountNE: count the number of non-empty cells
- PercentE: percent of empty cells
- PercentNE: percent of non-empty cells
- AverageNE: average over non-empty cells
Also added a subtle tweak that ignores an HTML comment tag ('<!--')
found between the table and the starting formula line. Being able to
wrap all the formula lines with an HTML comment prevents the formulas
from being rendered in Markdown/ReST output.
