Portable-wisdom

- Add transformer functions
- `beautify_hr` — converts lines of asterisks to horizontal rules
- `remove_duplicative_blockquotes` — removes magazine-style "pull quotes"
- `strip_links` — removes `a` elements
- `embed_images` — embeds remote web images
- Add quiet (`--quiet`) CLI option
- Add greyscale image (`IMAGE_GREYSCALE`), cache size (`CACHE_SIZE`) configuration options

- Improve code formatting to abide by PEP 8
- Improve README
- Support custom output filename (`--output`)
- Support custom style (`--style`)
- Add Travis CI configuration

- Improved README
- Fixed project metadata

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