Attempt to make merge format clearer
Per ingredient weight restrictions

Allow weight restrictions to be specified per-ingredient. This setting
overrides the total-weight restriction if higher.

More than one ingredient can be restricted. Both column (ingredient) names or
column indexes may be used to specify restrictions. An example command line
argument might be,

stats.py -t "flour=140,egg=34"

Which restricts flour to 140g and egg to 34g.