Make PDFDocument a node stream
Update demo to pipe to a node write stream instead of using deprecated write method
Update guide script for streams
Simplify image loading
Free memory after embedding images
Update guide for new stream based API
Update readme with stream info
Bump version and update PDF guide
Don't store all objects in memory, just offsets once they are written
Merge pull request #212 from devongovett/streams

API Change Announcement: Streams instead of write/output methods