Closes #4: Use phantomjs to provide a reliable path to 'phantomjs'.

To support this, The 'phantomjs' node package from was moved being an
optional to hard depedency.

It appears the 'phantomjs' package will detect if phantom is already installed, so
it doesn't inefficiently install a second copy.

Manually tested by with example.js.
Document that you depend `mkfifo` to be provided by the OS.
For #7, fix the memory leak in example.js by cleaning up the renderer when streaming is done.
Merge branch 'mkfifo-docs'
Merge branch 'phantomjs-path-issues'