Fix the return annotation for fetch_access_token
Return annotation description needs changing as well as type
Updated documentation.
By setting the type appropriately for the client, IDE's can use static analysis to help with autocompletion.
Revert "RAQ : Allow referral code to be supplied with all API calls."

This reverts commit 02a6c20839372d31c050c633be9f100442ba59e8.
cancel bills via the API
Merge pull request #28 from gocardless/pr/27

Fixed pull request for @RQuadling's comments
Merge pull request #24 from sampart/annotation-change

Fix the return annotation for fetch_access_token
Merge pull request #29 from gocardless/cancel-bill

cancel bills via the API
Allow the referrer (via the 'r' parameter) to be passed without signature failure.
Consolidate README links
More README changes
Added charge_customer_at
Updated the specs *grumble*grumble*grumble*
Merge pull request #30 from gocardless/charge_customer_at

Added charge_customer_at
Merge branch 'master' into Crowdcube_master

# By Grey Baker (2) and Kit (2)
# Via Grey Baker (1) and Kit (1)
* master:
  Updated the specs *grumble*grumble*grumble*
  Added charge_customer_at
  More README changes
  Consolidate README links
Added requirements to PHP docs
Adds line break and makes other readme changes
No more merge conflicts
Merge branch 'master' into Crowdcube_master

* master:
  Adds line break and makes other readme changes
  Added requirements to PHP docs
Update GoCardless.php

Corrected type for GoCardless::$client.