Ignore unknown variables and units in input string

[flinge]

Just simply ignore unknown text in the calculation string instead of showing an error. I.e. think of text as comments re what the numbers mean, like in this string, for example: (7000 revenue * 0.15 preCOVID margin - 400 dda - 2900 debt * 0.07 int rate) * (1 - 0.21 tax rate). https://erhanbaris.github.io/smartcalc-app/ can do it, please see attached.