Merge pull request #789 from python-gitlab/no-more-v3

docs: remove v3 support

docs/api-usage.rst

@@ -2,12 +2,7 @@
 Getting started with the API
 ############################
 
-python-gitlab supports both GitLab v3 and v4 APIs.
-
-.. note::
-
-   To use the v3 make sure to install python-gitlab 1.4. Only the v4 API is
-   documented here. See the documentation of earlier versions for the v3 API.
+python-gitlab only supports GitLab APIs v4.
 
 ``gitlab.Gitlab`` class
 =======================

docs/gl_objects/commits.rst

@@ -40,8 +40,7 @@ Create a commit::
     # See https://docs.gitlab.com/ce/api/commits.html#create-a-commit-with-multiple-files-and-actions
     # for actions detail
     data = {
-        'branch_name': 'master',  # v3
-        'branch': 'master',  # v4
+        'branch': 'master',
         'commit_message': 'blah blah blah',
         'actions': [
             {

docs/switching-to-v4.rst

@@ -8,24 +8,24 @@ GitLab provides a new API version (v4) since its 9.0 release. ``python-gitlab``
 provides support for this new version, but the python API has been modified to
 solve some problems with the existing one.
 
-GitLab will stop supporting the v3 API soon, and you should consider switching
+GitLab does not support the v3 API anymore, and you should consider switching
 to v4 if you use a recent version of GitLab (>= 9.0), or if you use
 https://gitlab.com.
 
 
 Using the v4 API
 ================
 
-python-gitlab uses the v4 API by default since the 1.3.0 release. To use the
-old v3 API, explicitly define ``api_version`` in the ``Gitlab`` constructor:
+python-gitlab uses the v4 API by default since the 1.3.0 release. If you are
+migrating from an older release, make sure that you remove the ``api_version``
+definition in you constructors and configuration file:
+
+The following examples are **not valid** anymore:
 
 .. code-block:: python
 
    gl = gitlab.Gitlab(..., api_version=3)
 
-
-If you use the configuration file, also explicitly define the version:
-
 .. code-block:: ini
 
    [my_gitlab]