Some way of combining multiple transforms using static-module

This is gonna be the most half-formed feature request I've ever posted on GitHub. Sorry!

**The problem to solve:** Since `static-module` works by parsing into an AST, transforming, and code-generating, it has a pretty significant overhead associated with it. For example: I have a script build using Browserify which takes about 8 seconds, where <2 seconds are spent compiling (TypeScript) and the remaining >6 seconds are spent in various transforms using `static-module` (`brfs` and `varlessify` (I wrote the latter)). I want to add another `static-module`-based transform, but I hesitate to add another 3 seconds to my incremental build time!

**Imagine a world** where multiple transforms using `static-module` could be combined into a single transform, thus significantly decreasing the performance impact. The source would only have to get parsed into an AST once! This would open the door to scalable use of tons of compile-time transformations. I'm not sure what the API for this would look like, but I have an inkling that it could _possibly_ be done entirely within `static-module` without requiring any changes to downstream modules like `brfs`, perhaps by returning an extra property on the result of `staticModule()`.

``` js
// a bunch of different transforms, more realistically pulled in separately from different modules
var brfs = staticModule({ { fs: ... }, ... });
var brfoo = staticModule({ { foo: ... }, ...});
var brbar = staticModule({ { bar: ... }, ...});

// combine them all
var massiveTransform = staticModule.combine(brfs, brfoo, brbar);
```

Thoughts?

Start by reviewing static-module's current transform API and the related Browserify transforms mentioned in the issue, including brfs and varlessify. Define a concrete composition API that parses and generates each source only once, then establish performance and compatibility checks showing that combined transforms work without requiring downstream changes.

Written by the indexing model from the issue text.