Add frmx new post command

[bobbermac]

Add support for generating stubbed content files, ready for editing.

The following commands should be supported:

• frmx new - alias for frmx new post
• frmx new post - new stubbed placeholder post of default content type
• frmx new post md - new stubbed placeholder post of Markdown content type
• frmx new post clj - new stubbed placeholder post of Clojure content type
• frmx new post edn - new stubbed placeholder post of EDN content type
• frmx new post html - new stubbed placeholder post of HTML content type
• frmx new post rfc - alias for frmx new post rfc5322
• frmx new post 5322 - alias for frmx new post rfc5322
• frmx new post rfc5322 - new stubbed placeholder post of RFC 5322 content type

All commands will generate a content file and a metadata file. The content file will be of the form specified in the command or will use the default type. The metadata file fill be in EDN format have have all supported keys stubbed with required fields indicated and optional fields set to an empty string, list, map, etc.

See ticket #1 for more details on these files.

[bobbermac]

Done.