Support single file snippets

[hay-kot]

Support ability to write single file snippets and use them from scaffold

Command

scaffold snip <snippet filename (optional extension)>

File Syntax

---
<scaffold file config>
---

<template>

Example

---
messages:
  pre: |
    # Example CLI scaffold

    This is an example CLI scaffold that can be used to generate a CLI application.
  post: |
    # You've generated a CLI application!

    You can now run the following commands:

    - `go run main.go` - Runs the main application and supports passing CLI args

questions:
  - name: "description"
    prompt:
      message: "Description of the project"
    required: true
---

Description: {{ .Scaffold.description }}