Deprecate resource & action level headers. Closes #57

Remove resrouce & action level headers example
Merge pull request #64 from apiaryio/1A

1A revision 3: Deprecate resource & action level headers
just a small typo
Remove Google Group mention
entinty entry origin, additional resourecs section origin
1B origin, additional glossary terms
payload term clarification
New specification structure. Remove superfluous header sections. Closes #59. Closes #57.