Write logic to generate project structure about 0.2.1-readme-dirs

[nchaloult]

I've written a first draft of some functionality.

What Works

• We can parse a response body from the Github API, ripping out the absolute paths of all directories in a repo e778235
• We can generate a tree-like printout of that directory structure 86da0ac

What Isn't Ready

• We aren't including comments about, or short descriptions of, commonly existing directories that we should be able to infer details about
  • i.e., if we see a src/ directory at the root of a repo, we can infer that source files live there, as opposed to other types of files in the repo
• We aren't taking advantage of any fancy markdown features yet
  • No relative links to each folder in the repo