Flag to reduce precision of GeometryField

DRF 3.8 support

Fix default widget for GeometryFilter

Using `forms.BaseGeometryWidget` will cause a IsADirectoryError, because
of an empty template_na...

Make ValidationError more user-friendly

removing every reference of olwidget & making admin widget as default geodjango widget.

[QA] Changed django test requirement from 2.0b1 to 2.0

[QA] Change django-filter test requirement to latest

Bring support for django 2.0 and drf 3.7

along the way drop django1.9 and 1.10

Corrected spelling mistake in README

Update README.rst

Latitude and longitude are documented in the wrong order for in_bbox filter.

Added support for GeometryCollection fields

Fixes for test_geojson_performance with DRF >=3.5

Fixes for Django 1.11

Changed in https://github.com/django/django/commit/50613d957a.

The default widget for `GeometryField` (`OpenLayersWidget`) was changed
to use `map_srid = 3857`...

[RFC] add tox.ini / support for pytest

Also adds Django 1.11 to Travis, closes #132.

Project is compatible with DRF 3.6

improve documentation of GeometryFilter

Fixed tests for django-filter 1.0.0

Avoid build breakage by eventual backward incompatible
changes introduced in django-filter futu...

Fixes https://github.com/djangonauts/django-rest-framework-gis/issues/120.

Being stricter will prevent future breakages of the CI builds.

Raised by DRF 3.5. Related to #119 - I've used a workaround here.

filter_overrides has been moved to the meta class in django-filter 0.15

README: fixed example for "Custom GeoJSON properties source"

The Django docs gives the following warning for `JSONField` (should be valid for `HStoreField` a...

Tested on django 1.10 prealpha successfully.
Closes #104

Closes #95

Those tests fail because of missing features in spatialite.

Related to #87
Newer version of Django are not compatible with python 2.6.