Implement translation for a markdown files

[vitonsky]

Some users needed in translation of markdown pages.
The typical use cases is a multi lingual README.md or dcos site.

We could split the markdown into AST and translate it by pieces, then use cache to translate only parts that have been changed.

User would control the splitting granularity. The obvious options is

• Whole document (no cache effectively)
• Top level nodes (paragraphs for example)
• Separate block nodes. (for example the paragraph, list item, etc)

The CLI API

The transly translate would translate everything found in config.

User would pass some flag to translate specific types of content like transly translate -t md,json

The config API

User would pass some glob to find markdown documents like

export default {
  markdown: ['./docs/**/*.md', './src/pages/.mdx']
}