[processing] fixed cmake
deleted EnumerateTableField description (redundant)
fix build error (followup ba8f3881)
[FEATURE] New expression functions for $currentfeature (returns current feature) and 'attribute' (returns value stored in specified field within a feature)
[FEATURE] New $atlasfeature expression function for returning the current atlas feature. Also clean up the expression groups and move some unrelated functions out of the 'Record' group.