Use default heuristics if required entries are not set in rule file

[manuelakuhn]

When entries are not defined in the rule file, would it make sense to apply the default heuristic? This would work as a fall back if required entries are not defined but also make live easier for users.

An example of why this might be helpful can be found in #192

[bpoldrack]

Agreed (in a way). What I outlined here: #191 (comment)
would solve this, since that is how subsequent application of several rules work.

For issue organization I'll leave this issue open, but close the other one.