infer_clone/infer/documentation/checkers/Impurity.md

This is an experimental inter-procedural analysis that detects impure functions. It is meant to be an improvement over the purity analysis with a negation on the issue types. For each function, impurity analysis keeps track of not only the impurity of the function but also some additional information such as which parameters/globals the function modifies. It models functions with no summary/model as impure. The analysis relies on Pulse summaries to determine impurity.