Elder.js esbuild

This is a tool I'm using on my own projects. It will change, it will break, I may even abandon it, use it at your own risk.

In your elder.js project:

todo:

[ ] hashed components (esbuild is tracking)
[ ] look at adding an additional export with _css to see if we can match Elder.js's current output. (basically impossible with current api)
[x] clean folder on initial build.
[x] remove dependencies/css on deletion of a svelte file.
[x] move css to a cache with sourcemaps instead of reading them from the file.
[x] modules with exported svelte files.
[x] rebundle the entire dependency tree on sub module change. (elder.js plugins with templates can use this same pattern.)
[x] clean up memory of caches.
[x] basic preprocess support....
[x] make sure that the css file is emitted to the right folder.