Write PST files

[mooijtech]

Add support for writing PST files.

• Write header
• Write header root
• Write block and node B-Trees
• Write B-Tree on Heap
• Write Heap-on-Node
• Write local descriptors (B-Tree nodes pointing to other B-Tree nodes)
• Write Property Context
• Write Table Context
• Write messages/attachments (make up the above from B-Tree)

CC @iredmail

[iredmail]

Cool. So you're starting working on it now?

[mooijtech]

Yes.