Invoke-PSScriptAnalyzer performance is very, very poor #197

Even for modules that contain a small number of commands (44 for one of my modules), Invoke-PSScriptAnalyzer is way too slow. When I ran it recursively on that module folder, it took just under 2 minutes (1 minute, 53 seconds) to perform the analysis. That's just horrible. Imagine a module that has 100+ commands? Please consider how you might take advantage of multiple threads/processes/jobs, or reducing the amount of redundant AST work that is being performed across similar rules to improve performance.

I find myself wondering if rules could be designed to plug into a single AST walkthrough instead of having each rule do its own AST searching/processing. Perhaps the notion of rule sets should be considered in order to permit certain rules to plug into a speedier process tailored to a particular area/feature/subset of PowerShell that is being analyzed. Those are just a few ideas that came to mind when thinking about how to solve this problem, but I imaging a profiling tool would identify at least a few areas where performance could be improved through less redundancy in code.