updated README.md
minor updates
restructured PortalTokenSecurityHandler to match AGOLTokenSecurityHandler
resolved spelling issue in token url
Merge branch 'master' of https://github.com/Esri/ArcREST
Merge branch 'master' of https://github.com/Esri/ArcREST

Conflicts:
	README.md
Added referer url to functions to support QA and Dev ArcGIS environments
Merge branch 'master' of https://github.com/Esri/ArcREST
Merge pull request #20 from MikeMillerGIS/master

Restructured for consistency and calculated referer url for dev enviroments