new directives for including files

I submitted an issue here:
https://github.com/TrevorBurnham/connect-assets/issues/73

This patch introduces two new keywords: 
#=include FILE for including file to source
#=include_str FILE for including file with escaping some special characters

My patch just replacing #=include with file's contents. It doesn't register FILE as a dependency (I dont know how to do it). So, there might be some problems with it.

I didn't include compiled snockets.js because I have custom version of compiler and there will be too many unrelated diffs.

I couldn't write tests because of this:

```
squogre:snockets:% cake test
The "sys" module is now called "util". It should have a similar interface.

/home/alex/node_modules/snockets/node_modules/watch-tree/lib/watchers/stat.js:148
        throw err;
              ^
Error: ENOTDIR, not a directory 'test/integration.coffee'
```

But it works for me... so far so good. And it definitely better than nothing.