Merge pull request #25 from adlnet/master

Sync up!
Update xAPI.md

5.1-5.3 - note State language removed from 5.1 to go generic across documents.  Requirement was "added" as it existed within the table.
5.3 saw non-requirement "shoulds" go into details, the rest separated into requirements.  Requirements around IRI "owners" and the "permission" were dropped in favor of language just saying that they should be controlled.  This "requirement" may be a bit much, but didn't want to risk moving to a non-patch version.
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4.4 up to requirements
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5.4 requirements done, except the last requirement which should be clarified.
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Section 5 - Typos corrected, some requirements removed/editted
updated attach section about subs
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Attempt on the document key requirement
'verb' is now an object.

This is a fix missed at the time of filing #253.
Added the missing X-Experience-API-Version field header.
Fixed the value of the Authorization field header, according with the example.
Using capital letters for the HTTP header field names, just for readability since
field names are case-insensitive as per RFC 2616 (§4.2, "Message Headers").
Designating the encoding is somewhat redundant for JSON.
The default encoding for JSON is UTF-8, as per RFC 4627 (§3, "Encoding").
Moved Version from "1.0" to "1.0.0" as per PR comment.

Please note that 1.0 is equivalent to 1.0.0 as per spec:
https://github.com/adlnet/xAPI-Spec/blob/097552f8a9deab6ac85ba3ffa86d18fdffeb9ca6/xAPI.md#lrs-requirements-4.
SHA-2 type is not "base64": better a string of 64 hexits (SHA-256).
Trivial case typo: "integer" => "Integer".
Merge pull request #363 from phamdt/master

fix small typo: idenfier -> identifier
Merge pull request #360 from scara/Attachments_SHA2_Type_Should_Be_String_Not_Base64

SHA-2 type is not "base64": better a string of 64 (SHA-256) hex digits (hexits).
Merge pull request #359 from scara/Appendix_A_Wrong_Example_Statement_Using_Bookmarklet

Appendix A: wrong example statement using bookmarklet
Merge pull request #358 from ljwolford/substmt

updated attach section about subs
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Updated to remove requirement (from the section, still exists in other language elsewhere)
Merge pull request #355 from andyjohnson/master

Section 5 Edits/Formatting
Fix capitalisation of openid