Laterpay-client

* Dialog API Wrapper is [deprecated](http://docs.laterpay.net/platform/dialogs/third_party_cookies/).
* `get_buy_url()`, `get_add_url()`, `get_login_dialog_url()`, `get_signup_dialog_url()`, and `get_logout_dialog_url()` have a new `use_dialog_api` parameter that sets if the URL returned uses the Dialog API Wrapper or not. Defaults to True during the Dialog API deprecation period.
* `ItemDefinition` no longer requires a `cp` argument.

* Exceptions raised by `urlopen` in `LaterPayClient._make_request()` are now logged with `ERROR` level using `Logger.exception()`.
* Added `timeout_seconds` (default value is 10) param to `LaterPayClient`. Backend API requests will time out now according to that value.
* Removed deprecated `laterpay.django` package.
* Removed deprecated `vat` and `purchasedatetime` params from `ItemDefinition.__init__()`. This is a backward incompatible change to `__init__(self, item_id, pricing, url, title, cp=None, expiry=None)` from `__init__(self, item_id, pricing, vat, url, title, purchasedatetime=None, cp=None, expiry=None)`.
* Removed deprecated `add_metered_access()` and `get_metered_access()` methods from `LaterPayClient`.

* Standardised the usage of the (internal) `product` API (it was usable via path or parameter, and we're deprecating the path usage)

* Deprecating the `vat` parameter in `ItemDefinition` because of new [EU law for calculating VAT](http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32006L0112&from=DE)
* Deprecated `LaterPayClient.get_metered_access()` and `LaterPayClient.add_metered_access()` methods.
* Added `return_url` / `failure_url` parameters for dialogs: http://docs.laterpay.net/platform/dialogs/

* Support for Python 3.3 and 3.4 (https://github.com/laterpay/laterpay-client-python/pull/1)
* Improved documentation coverage
* Dropped distutils usage
* Fixed [an issue where omitted optional `ItemDefinition` data would be erroneously included in URLs as the string `"None"`](https://github.com/laterpay/laterpay-client-python/pull/19)
* Added deprecation warnings to several methods that never should have been considered part of the public API
* Deprecated the Django integration in favour of an explicit [`django-laterpay`](https://github.com/laterpay/django-laterpay) library.
* Added support for [expiring items](hhttp://docs.laterpay.net/platform/dialogs/)

Existence