New log format

Code for #791.

New output for `jekyll build`:

```text
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:

```text
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`:

```text
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.
```

New output when there's no `_config.yml` file:

```text
           WARNING: Error reading configuration. Using defaults (and options).
Configuration file: (INVALID) /Users/parkermoore/code/jekyll-clean/sample_site/_config.yml
            Source: /Users/parkermoore/code/jekyll-clean/sample_site
       Destination: /Users/parkermoore/code/jekyll-clean/sample_site/_site
      Generating... done.
```