Abstract/Introduction: Incoporate feedback from Steve Huston's review

Incorporate feedback from Steve Huston's review of the Abstract and Introduction (Part 0) of the document.

This JIRA covers small changes and minor corrections, typos, grammar and punctuation errors within the Abstract and Introduction (Part 0). In particular it is aimed at addressing the following points from Steve's mail(s):

Page 1, Abstract:
First para, first sentence: "internet protocol" should not be capitalized,
nor should "business messaging."

4th sentence: insert comma between "efficient" and "binary" and between
"binary" and "peer-to-peer"

Part 0, sect 1, 1st sentence: "internet protocol" and "business messaging"
should not be capitalized.

Part 0, sect 1, 2nd para:
1st sentence replace with "AMQP is comprised of several layers."
(Use third person consistently)

2nd sentence replace with "The lowest level contains an efficient, binary,
peer-to-peer protocol for transporting messages between two processes over
a network.
3rd sentence "The next level contains" instead of "Secondly we define"

Part 0, sect 1.1 "keywords" should be "key words" per RFC 2119