Fixes small bug in ShoppingCart, triggered if the session goes expires and then a user clicks a remove product link
Merge pull request #282 from markguinn/patch-shoppingcart-error

Fixes small bug in ShoppingCart, triggered if the session goes expires a...
Allow showing all products if ProductCategory page_length is 0.
Documentation updates
Update CheckoutStep_Address.php: function setbillingaddress

Remove $step as it is not defined in the setbillingaddress function.  
This change seems to work well in browser, however, testBillingAddress in SteppedCheckoutTest fails.
Merge pull request #284 from AntonyThorpe/patch-1

Update CheckoutStep_Address.php: function setbillingaddress
Update _config.php

Additional unnecessary argument.  The function setupSteps, within class SteppedCheckout, only requires $steps.
Merge pull request #285 from AntonyThorpe/patch-2

Update _config.php
Added a bunch of add-on modules to README
Try again
Update README.md
README update
Reordered the README file a bit more
Update README.md
Update README.md
Update CONTRIBUTING.md
Documentation overhaul. Updated to be structured better, and more consistent with the current state of the module.
Updated payment documentation
Further documentation improvements
Updated CartForm to work with Buyables, rather than just Product.
Updated Custom Products documentation to include some additional notes about what to implement.
Thanks @wildflower for finding this.