Support manual into output that is documentation other than the API reference #102

{
  "source": "./src",
  "destination": "./doc/",
  "manual": {
    "overview": "./manual/overview.md",
    "installation": "./manual/installation.md",
    "usage": "./manual/usage.md",
    "example": "./manual/example.md",
    "faq": "./manual/faq.md",
    "changelog": "./CHANGELOG.md"
  }
}