Merge pull request #1 from darinmorrison/master

Add README.md
Merge pull request #4 from darinmorrison/master

reorganize into library structure
Give prepend in terms of insert
Minor improvements

- Dereference self before matching (I still don't know the difference
  here, but it seems more in line with tradition)

- Use the "smart" Append function in concat
Further modularizing
Remove commented stuff I didn't mean to commit
only expose what I need from string_utils
Data abstraction
Minor style improvement
Rename pretty module to doc (we had pretty::pretty, want pretty::doc)
Add a working example (Wadler's trees)
collapse extra doc mod