CH02::Alice pays Bob: change example from laptop to podcast episode

Before earlier edits, the second edition text for this chapter was about
buying a cup of coffee.  The edits changed it to a laptop.  The risk
profile of a cup of coffee and a laptop are different, making some parts
of the text problematic, e.g. Bob accepting payment without waiting for
confirmation.

This update replaces the example with Alice buying a premium podcast
episode, which has a very low risk profile.

ch02.asciidoc

@@ -69,14 +69,14 @@ Alice, introduced in the previous chapter, is a new user who has just
 acquired her first bitcoins. In <<getting_first_bitcoin>>, Alice met with
 her friend Joe to exchange some cash for bitcoins. Since then, Alice has
 bought additional bitcoins.  Now Alice will make
-her first retail transaction, buying a laptop from Bob's online store.
+her first retail transaction, buying access to a premium podcast episode from Bob's online store.
 
 Bob's web store recently started accepting bitcoin payments by adding a
 bitcoin option to its website. The prices at Bob's store are listed in
 the local currency (US dollars), but at checkout, customers have the
 option of paying in either dollars or bitcoin.
 
-Alice shops for a laptop and proceeds to the checkout page. At checkout,
+Alice finds the podcast episode she wants to buy and proceeds to the checkout page. At checkout,
 Alice is offered the option to pay with bitcoin, in addition to the
 usual options. The checkout cart displays the price in US dollars and
 also in bitcoin (BTC), at Bitcoin's prevailing exchange rate.
@@ -199,12 +199,12 @@ previous transaction's output as its input. In the previous chapter,
 Alice received bitcoin from her friend Joe in return for cash. That
 transaction created a bitcoin value locked by Alice's key. Her new
 transaction to Bob's Store references the previous transaction as an
-input and creates new outputs to pay for the laptop and receive change.
+input and creates new outputs to pay for the podcast and receive change.
 The transactions form a chain, where the inputs from the latest
 transaction correspond to outputs from previous transactions. Alice's
 key provides the signature that unlocks those previous transaction
 outputs, thereby proving to the Bitcoin network that she owns the funds.
-She attaches the payment for the laptop to Bob's address, thereby
+She attaches the payment for the podcast to Bob's address, thereby
 "encumbering" that output with the requirement that Bob produces a
 signature in order to spend that amount. This represents a transfer of
 value between Alice and Bob. This chain of transactions, from Joe to
@@ -370,10 +370,10 @@ View the http://bit.ly/1tAeeGr[transaction from Joe to Alice].
 ====
 
 As you can see, Alice's wallet contains enough bitcoin in a single
-unspent output to pay for the laptop. Had this not been the case,
+unspent output to pay for the podcast. Had this not been the case,
 Alice's wallet application might have to "rummage" through a pile of
 smaller unspent outputs, like picking coins from a purse until it could
-find enough to pay for the laptop. In both cases, there might be a need
+find enough to pay for the podcast. In both cases, there might be a need
 to get some change back, which we will see in the next section, as the
 wallet application creates the transaction outputs (payments).
 
@@ -393,7 +393,7 @@ for a signature from Bob.
 
 This transaction will also include a second output, because Alice's
 funds are in the form of a 0.10 BTC output, too much money for the 0.015
-BTC cup of laptop. Alice will need 0.085 BTC in change. Alice's change
+BTC podcast. Alice will need 0.085 BTC in change. Alice's change
 payment is created by Alice's wallet as an output in the very same
 transaction as the payment to Bob. Essentially, Alice's wallet breaks
 her funds into two payments: one to Bob and one back to herself. She can
@@ -670,7 +670,7 @@ thus providing assurance that the miners accepted it as valid.
 
 Bob can now spend the output from this and other transactions. For
 example, Bob can pay a contractor or supplier by transferring value from
-Alice's laptop payment to these new owners. Most likely, Bob's bitcoin
+Alice's podcast payment to these new owners. Most likely, Bob's bitcoin
 software will aggregate many small payments into a larger payment,
 perhaps concentrating all the day's bitcoin revenue into a single
 transaction. This would aggregate the various payments into a single