general editing: made datetime.rfc3339 reference back to section describing it, and renamed it to remove any possible confusion.
general editing: edited string.rspec data type section and made string.rspec reference back to section describing it, and renamed it to remove any possible confusion.
fixed markup of rspec_version section title and tweaked some texted in the note about sliver expiration time
improved description of sliver info list
Merge pull request #40 from wvdemeer/more-general-editing

Text improvements