wordsmithing ch02.asciidoc

Many small grammar updates.  
Please carefully review paragraph beginning "Transactions are like". Previous text was backwards about debits and credits in this case of what is essentially a balance sheet (i.e., asset-based accounts versus income and expenses).  In this case, the Inputs on the left are the credits (although in accounting debits are conventionally shown on the left).  However, I'm not 100% happy with my revision either.  Perhaps it can be further improved and without relying on the reader to really understand anything about debits and credits.

Please review carefully the bullet "Mining creates new bitcoins in each block".