Javascript minifier implemented in rust.
# Cargo features
## `debug`
If you enable this cargo feature and set the environment variable named
`SWC_RUN` to `1`, the minifier will validate the code using node before each
step.
Note: Passes should be visited only with [Module] and it's an error to feed
them something other. Don't call methods like `visit_mut_script` nor
`visit_mut_module_items`.