Merge pull request #2 from taenyon/update

merge from 'master' branch of original repository.
Fixes a wrong field name of get_adgroups_* methods.
Merge pull request #3 from taenyon/bugs

Fixes a wrong field name of get_adgroups_* methods.
Restore fields parameter for get_adgroups_by_* methods.
Fixes miss typing in the code.
Add new method for creating adset.
Add feature to create custom audience.
Fixes a wrong syntax.
Fixes miss spell.
Fixes parameter format as json for create_audience() method.
Chagne create_custom_audience() method to support other subtypes and add new method for creating custom audience from website.
Add feature to create lookalike audience.
Modify create_custom_audience() method to suport with facebok specifications.
Fixes syntax error.
Add new functions for getting custom audience and remarketing pixel.
Adjust some codes in order to comply the rule of pep8.
Merge pull request #17 from taenyon/update

Add new functions for custom audience and remarketing pixels.