Use Grasp to make post-compilation replacements

I wanted to be able to use Grasp instead of string replacement, and ended up adding the `export` functionality with bd51feb2da71077bfbf72d0ce8b4a52f167d7366. I'm sure there will need to be changes made, so I pushed my branch to the main repo – please feel free to make any changes you think are necessary before we merge this in.

Additionally I wrote a package around your Grasp wrapper – @mquandalle please feel free to clone my repo and publish it under your account, as you're the one that wrote the original wrapper. Please let me know what you want to have done with this code before it's merged in! You can [look at the example app](https://github.com/christianbundy/meteor-harmony-example/tree/add-grasp) if you'd like.