A big reorganization, and some new stuff too

[ttmc]

• New page about how to construct a transaction
• Put transaction examples on separate page
• New pages for version, operation, metadata
• Wrote more about how to compute a fulfillment & a fulfillment string
• Noted the constraints on the separators in the IPDB Protocol standard JSON strings
• Switched to talking about building associative arrays rather than JSON objects, to be more programming language agnostic
• Put the high-level structure of a transaction on the index page for transactions