Fix #8: Allow standard input

The tools under `bin/` now accept input from STDIN.  

 * Input can be piped in (`cat file.cson | cson2json -`)
 * Input can be redirected (`cson2json - < file.cson`)

There are a few caveats:

 * **There are no tests for the executables.**
  
  (I tried, but couldn’t.  I’m sure it’s be easy, but I’m continuing to learn Node, and it has a myriad of test frameworks.)

 * **Executables only read from STDIN when passing `-` as the only argument.**

 * **If `-` is passed without actually piping (or redirecting) anything**, the program waits for input until it receives <kbd>CTL</kbd>+<kbd>D</kbd>.

  (I’d like to fix this in the future.  For now, at least it’s consistent with the behavior of `cat - `.  Hitting  will tell the program to stop waiting.)