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 pull request #6 from markstos/phantomjs-path-issues

Closes #4: Use phantomjs to provide a reliable path to 'phantomjs'.
Fix typo: s/OS/OS X/
Merge pull request #9 from markstos/fix-memory-leak

For #7, fix the memory leak in example.js by cleaning up the renderer when streaming is done.
Merge pull request #8 from markstos/mkfifo-docs

Document that you depend on `mkfifo` to be provided by the OS.
Merge pull request #5 from aredo/master

add default option for weight and height
Update default values on README.
Add timeout to deferred render and ensure no double render.
Check renderable before creating property.
Reset page after every render and fix typo.
Resume to avoid memory buffering.