New log format

Code for #791.

New output for `jekyll build`:

```
Configuration file: /Users/parkermoore/code/jekyll-clean/site/_config.yml
            Source: /Users/parkermoore/code/jekyll-clean/site
       Destination: /Users/parkermoore/code/jekyll-clean/site/_site
      Generating... done.
```

No longer warns you if you have no config file:

```
Configuration file: none
            Source: /Users/parkermoore/code/jekyll-clean/sample_site
       Destination: /Users/parkermoore/code/jekyll-clean/sample_site/_site
      Generating... done.
```

New output for `jekyll build --watch`:

```
Configuration file: none
            Source: /Users/parkermoore/code/jekyll-clean/sample_site
       Destination: /Users/parkermoore/code/jekyll-clean/sample_site/_site
 Auto-regeneration: enabled
      Regenerating: 1 files at 2013-02-03 20:35:19                  ...done.
      Regenerating: 1 files at 2013-02-03 20:35:23                  ...done.
      Regenerating: 1 files at 2013-02-03 20:35:24                  ...done.
^C     Halting auto-regeneration.
```