Add doc/OrderbookExample.txt
Represent the OrderbookExample.txt in the data structure in YAME.
""
All test cases are passed using the following code from within the EShell
    observer:start().
    yame:test().
    rr(yame).
    pid(0,49,0) ! #order{stock = "StockX", trader = 999, bid_or_ask = bid, amount = 55, price = 116}.
    ...
""
Add file-level header comment block
""
""