Add 'progress' to 'result'

I have a use case on a real live project to report both 
page progress and score for a SCORM-style course. I imagine 
this is a common use case. I'm surprised this hasn't come up 
before actually. 

I think the solution proposed is quite neat and simple. I don't
think an extension would be appropriate for something so common.
changed language of score and progress; reordered result properties

I did consider having just one score object property and changing its use based on verb, but since we have separate completion and success properties, I thought separate progress and score properties made sense too. 
full stops
Added 'units' property to 'score' object

also fixed a mis-written </tr> and inconsistent capitalisation. 
Paul's changes, without whitespace-only changes
Merge pull request #41 from bscSCORM/bsc_paul

Paul's changes, without whitespace-only changes
condensed rewrite of chapter 6.2 Versioning

Weeded out a possible contradiction where one might understand that all
versions prior to 1.0 are considered incompatible, but there was also a
note on preserving backward compatibility with 0.95
condensed rewrite of chapter 6.2 Versioning (step 2)

added possibility to allow for versions below 1.0 to be valid.
Merge pull request #42 from paul-esch/master

condensed rewrite chapter 6.2 Versioning
removed progress and units
Changed activity to experience. Toned down reference to extension.
clarified definition of Activity

One of the todos in the meeting minutes of the recent workgroup meeting.
Added an example to clarify possible confusion about interpretation of
'Activity'.
added descriptions for MUST SHOULD MAY

These three words are used throughout the document, but a description
was nowhere given.
As a side note: I'm not a native speaker of English so apart from
correctness and completeness, please check grammar.
added entry MUST SHOULD MAY to the index of definitions

however I suggest leaving the index of definitions out of the document
completely, since the list is not long at all and immediately below the
index, so it doesn't add very much.
removed last TCAPI reference and replaced with xAPI
Merge pull request #50 from nhruska/master

removed last TCAPI reference in examples and replaced with xAPI
Merge pull request #49 from paul-esch/master

Chapter 3: Definitions
Merge pull request #40 from garemoko/pageViewTracking

Page view tracking
Merge pull request #10 from adlnet/master

update garemoko master to adlnet