adding simple-parse example

In partial response to #133, I've created `examples/simple_parse.c`, a simple standalone program that parses a line of text into a json_t structure and prints it.  (As a by-product, simple_parse.c has a `print_json()` method that recursively walks and prints a `json_t` object.)

What's missing is a makefile for the example directory and extensions to the other makefiles -- I'm not familiar enough with CMake or Makefile.am to confidently create them.
`getline()` isn't the best function to be used here because it's not portable. How about simply using `fgets()`?