eventual consistancy

* Created a section for common requirements when PUT-ing or POST-ing statements,
moved existing common requirements to that section
* Added eventual consistancy requirements
add section on data constraints
attempt to deal with spacing issue
more space fiddling
minor wording change
tidy up
Merge pull request #171 from bscSCORM/eventual

eventual consistancy
Merge pull request #177 from fugu13/tidyup

Just a small bit of tidying up
Merge branch 'master' of https://github.com/adlnet/xAPI-Spec
Merge branch 'master' into dataconstraints
Rearrange LRS requirements related to API parameters for clarity and applicability
fix typo in header name
Merge pull request #176 from fugu13/dataconstraints

Add a section on data constraints
clarified "conflict with verb display"

resolve issue: https://github.com/adlnet/xAPI-Spec/issues/180
updated version # to 1.0.0
updated example signature based on new ver # in example statement
reference Semantic Versioning

Small change to actual requirements, mainly the declaration that we will conform
to Semantic versioning impacts future releases.
activity definition / metadata clarification
Yet another bunch of minor cleanups
Rephrased as per PR comments