Simple Parser for Text File Lines

[pmbittner]

To analyze source code files we have to be able to parse text files to our simple abstract syntax trees from issue #50.
The idea is to create parser with the following interface

public static AST<LineGrammar, String> parseDirectory(java.nio.Path path) {
    /**
      *Traverse the given directory recursively and read the lines of all non-binary files (e.g., .java, .cpp, .txt, ...).
      * Create a node in the tree for each directory, file, and the lines in that file,
      * such that the directory structure is mirrored in the returned tree.
      */
}