* Add new `stack_processor` parameters for `get_flame_graph`
* A `stack_processor` is a class inherited from `StackProcessor` which can implement custom processing for stacks and frames, usually with the goal of changing the flamegraph to something more readable or to change what the flamegraph will show
* Added a NodeJSStackProcessor, which can be used to improve Node.js flamegraphs taken with Linux perf
* Added a NodeJSPackageStackProcessor, which can be used to group frames by Node.js module on profiles taken from Linux perf