Various cleanup / minor issues

* 7.1 Error codes needs some "MUST" https://github.com/adlnet/xAPI-Spec/issues/97
    * Tightened the language to "most appropriate" (400 would be appropriate anywhere 403 would be, but 403 should be used when it's "most appropriate").
    * Removed language which implied 400 return codes were optional, or that other return codes could not appear on any resource

* stored shouldn't be in the future, remaining issue was actually the sub-statement reference, removed https://github.com/adlnet/xAPI-Spec/issues/105
* stored/timestamp precision https://github.com/adlnet/xAPI-Spec/issues/83
attachments should specify binary

Issue: https://github.com/adlnet/xAPI-Spec/issues/107

* attachment's MUST specify a transfer encoding of binary
* LRS SHOULD assume binary transfer encoding even if it was (incorrectly) not specified

There is no need to allow other transfer encodings as these messages are to be sent over HTTP which supports binary
fix: remove lines that should have been removed in query PR

The query overhaul removed the overloading of the "object" query parameter as either agent or activity, and
this was understood by reviewers -- these lines make no sense here and should have been deleted.

I think everyone missed this on review because these lines weren't added or removed.
Merge pull request #123 from bscSCORM/query_fix

fix: remove lines that should have been removed in query PR
Merge pull request #121 from bscSCORM/cleanup

Various cleanup / minor issues
0.95 to 1.0 changes list added
Merge pull request #124 from garemoko/changelog

0.95 to 1.0 changes list added
Merge pull request #122 from bscSCORM/binary

attachments should specify binary
standardized headings in sections 2 and 3
Merge pull request #125 from garemoko/section2&3headings

standardized headings in sections 2 and 3