Command line blogging

This adds support for easier command-line blogging, with ./create-post.rb

Example help output:

```
Usage: create-post [options] "Blog title here."
    -a, --author          Author name (default: garrett)
    -d, --date            Custom datetime (default: 2014-10-01 16:35:28 CEST)
    -e, --editor          Custom editor (default: vim)
    -t, --tags            Comma-separated list of tags
    -n, --no-browser      Disable browser
    -h, --help            Display this help message.
```

It defaults to the current user, current time, and $EDITOR (or system text editor) and system browser. It should be cross-platform, but I have only tested it on Linux (Fedora specifically).