Update README.md

Added link to EnvPane for Mac OSX users to set environment variables.
Add support for httr OAuth2.0 authentication
Add support for httr OAuth2.0 authentication
Support httr OAuth 2.0 authentication and changes to JSON to R conversion
Update README.md

Using CRAN version of httr now which supports OAuth2.0
Update README.md
Add httr oauth cache file to the list of files that git should ignore
Merge branch 'master' of https://github.com/jdeboer/ganalytics into dev

Conflicts:
	R/GaApiRequest.R
	R/GetGa.R
Refactor API request function to allow for the case of no query parameter.
Migrate to Metta data API and use httr for OAuth authentication
Metta data API request and refactor OAuth handler