Implement automatic spell-check for docs (#688)

* [WIP] Implement automatic spell-check for docs

fixes #663

The only thing unclear to me so far is how the output of `make spelling`
should be checked - is there a possibility to check for a file (i.e.
`_build/spelling/output.txt`) to be empty, and report a failed build
otherwise?

* fix typo in requirements.txt

* add enchant library

* travis should report errors, order spelling wordlist

* change travis.yml to easier troubleshoot build issues

* fixed more typos, added more words

* add more words, fix more typos

* added more words

* added more words

* revert changes to .travis.yml

doc/development/implementation/logging.rst

@@ -19,7 +19,7 @@ To actually log an action, you can just call the ``log_action`` method on your o
    order.log_action('pretix.event.order.canceled', user=user, data={})
 
 The positional ``action`` argument should represent the type of action and should be globally unique, we
-recomment do prefix it with your packagename, e.g. ``paypal.payment.rejected``. The ``user`` argument is
+recommend to prefix it with your package name, e.g. ``paypal.payment.rejected``. The ``user`` argument is
 optional and may contain the user who performed the action. The optional ``data`` argument can contain
 additional information about this action.
 

doc/development/implementation/models.rst

@@ -1,6 +1,8 @@
 .. highlight:: python
    :linenothreshold: 5
 
+.. spelling:: answ contrib
+
 Data model
 ==========
 

doc/development/implementation/settings.rst

@@ -35,7 +35,7 @@ Forms
 -----
 
 Hierarkey also provides a base class for forms that allow the modification of settings. pretix contains a
-subclass that also adds suport for internationalized fields:
+subclass that also adds support for internationalized fields:
 
 .. autoclass:: pretix.base.forms.SettingsForm
 
@@ -65,4 +65,4 @@ Plugins can add custom hardcoded defaults in the following way::
 Make sure that you include this code in a module that is imported at app loading time.
 
 .. _django-hierarkey: https://github.com/raphaelm/django-hierarkey
-.. _documentation: https://django-hierarkey.readthedocs.io/en/latest/
+.. _documentation: https://django-hierarkey.readthedocs.io/en/latest/

doc/development/implementation/urlconfig.rst

@@ -67,7 +67,7 @@ available as ``plugins:sendmail:send``.
 Generating a URL for the frontend is a complicated task, because you need to know whether the event's
 organizer uses a custom URL or not and then generate the URL with a different domain and different
 arguments based on this information. pretix provides some helpers to make this easier. The first helper
-is a python method that emulates a behaviour similar to ``reverse``:
+is a python method that emulates a behavior similar to ``reverse``:
 
 .. autofunction:: pretix.multidomain.urlreverse.eventreverse
 
@@ -82,5 +82,5 @@ Implementation details
 ----------------------
 
 There are some other caveats when using a design like this, e.g. you have to care about cookie domains
-and referer verification yourself. If you want to see how we built this, look into the ``pretix/multidomain/``
+and referrer verification yourself. If you want to see how we built this, look into the ``pretix/multidomain/``
 sub-tree.