add "rename" option, bump nunjucks dep to 1.0.0 to fix runtime error

## add "rename" option

This adds a task option `rename` that is called once per template file and used to populate the `name` option to `precompile`.

Example:

```
var path = require('path');
...
nunjucks: {
  precompile: {
    options: {
      rename: function(src) {
         return path.basename(src);
      },
  },
```

## bump nunjucks dep to 1.0.0 to fix runtime error
Before upgrading Nunjucks to 1.0.0, I was hitting the following error:

![screen shot 2013-10-29 at 4 29 53 pm](https://f.cloud.github.com/assets/1527302/1433475/262d4b82-40f5-11e3-9881-8ae59cd28ead.png)