Authority requirement cleanup

Pulled out some of the more basic requirements for authority to the top of the section.

The rest probably could still use some re-formating, but I suggest this is a useful step worth merging, since it pulls some important points to the top.
Rewrite of 4.1.3 Verb

As a sort of ‘clean slate decision' I left out references to previous
versions of the spec. I feel this has only a historic meaning to the
limited number of people that are aware of / were involved in previous
versions of the spec. In anyone feels this should be included, leave a
comment.

Possible confusion: The description of the ID property says a URI should
be human-readable. Yet, "tag:example.com,2012:xQr73H" is given as an URI
example a little earlier and that is not very human-readable. Is this a
contradiction?
Added: Reading guidelines for the non-technically inclined.

One of my intentions is to make this technical document as
'approachable' as possible for folks such as instructional designers,
project managers or even commercial people. To address them directly, I
added this little paragraph.
made this line more generic.
made some corrections based on Andrew's comments
removed unclear example

as agreed with Andrew.
Merge pull request #91 from paul-esch/master

rewrite of 3.1.4 Verb, and a small note to the not-so-technical readers.
Merge pull request #90 from bscSCORM/authority

Authority requirement cleanup
Rewrite of 4.1.11 Attachments

Well-structured original to begin with, but this section also contained
many sentences that were either descriptions, procedures or a
combination of both.(For example, the paragraph 'Transmission Format' in
the original). I took a stricter approach in separating that.

The Rationale-paragragh is also aimed at non-techies and as such
contained much too complex content. This was placed elsewhere in the
section.

Took out he unclear term "common requirements", this does not define
well what the requirements relate to (statements, attachments, LRS,
client?) and put those under the header "requirements for statement
streams that include attachments".

Made a literal copy-n-paste of the code examples, but they didn't look
good when previewing. Sorry if they turn out to be wrong on Github.
Someone more experienced with Github should please correct this.
Merge branch 'master' of https://github.com/adlnet/xAPI-Spec
Merge pull request #15 from paul-esch/master

Fork Paul's repo