Update ch01.asciidoc, What is bitcoin 3rd para

Made a few implied points more explicit and changed "transaction" to "address" in a few occasions where it was more appropriate
for e.g.  
"Users of bitcoin own keys which allow them to prove ownership of transactions in the bitcoin network, unlocking the value to spend it and transfer it to a new recipient. " to 
"Users of bitcoin own keys which allow them to prove ownership of addresses in the bitcoin network. Unlocking these addresses, unlocks any value associated to it and grants the user the ability to spend and thus transfer value from it."

Do key holders really own transactions? when someone transfers bitcoin to a user's address, is that transaction really theirs? Isn't it more appropriate to say that the bitcoins associated to their address is theirs.

"Unlocking value to spend it and transfer it to a new recipient"
here unlocking value implies the "value to spend it" instead of "spend the value", also, spend and transfer seem redundant and hence doesn't garner the "and' but rather a "thus" feels more correct. I may be acting as a stickler here, but the last line about transferring to a new recipient can be violated by transferring to an old recipient :-), so I changed it to "unlocks any value associated to it and grants the user the ability to spend and thus transfer value from it. "