Environment authentication

Additions

• You can now set your GA_CLIENT_ID, GA_CLIENT_SECRET in environment arguments and they will be added to the project options on startup.
• Authenticate on startup with GA_AUTH_FILE pointing to your cache file.
• Add support for "today" and "yesterday" date values in anti_sample (#112)
• Add that max is ignored during anti_sample=TRUE (#111)

Bug fixes

• Fix bug of argument match in multi_select(#99 - thanks @sdhaus)
• Fix bug for data dimensions starting with a number (#100 - thanks @kennyengci)
• Remove hourly anti-sampling as it doesn't work
• Use tidy eval instead of dplyr underscore funcs (thanks @kiendang)
• Fix multi-channel funnels raising error when no data available (thanks @octaviancorlade)
• Fix NULL validaation if no results returns in v4 API (#81 again - thanks @ricardopinto)