Fixes#86
This allows the formula line to be evaluated, even if there is a single
empty line after the table. The "empty" line is allowed to contain
whitespace, but nothing else.
The formula will evaluate if triggered on the table, the empty line, or
the formula lines.
* 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.
