Better handling of boolean parameter.

Added internal function to handle boolean parameters. The code is
expecting them to be bassed as boolean type but it will also check for
their string representation ('true' and 'false').
Merge branch 'master' of github.com:Traackr/traackr-api-php
Fix a few typos. Unit test now passing.
Add support for 'enable_audience_aggregation'

Add support for 'enable_audience_aggregation' on /influencers/search