Increase major version due to the API change

The API should be backward compatible but the overzoom extension should rather
be promoted with a major version number change.

.appveyor.yml

@@ -1,4 +1,4 @@
-version: 2.7.{build}
+version: 3.0.{build}
 
 configuration:
   - Release

README.md

@@ -41,8 +41,8 @@ reader.read(&img);
 you will get 1024x1024px tiles with a pixel ratio of 2 (= HiDPI tiles).
 
 ### Overzoom
-Since version 2.7 tile overzoom is supported. If you set *format* to
-`$zoom;$overzoom`:
+Since version 3 of the plugin tile overzoom is supported. If you set *format*
+to `$zoom;$overzoom`:
 ```cpp
 QPixmap pm;
 QByteArray fmt(QByteArray::number(zoom) + ';' + QByteArray::number(overzoom));

pbfplugin.pro

@@ -2,7 +2,7 @@ TARGET  = pbf
 TEMPLATE = lib
 CONFIG += plugin
 QT += gui
-VERSION = 2.7
+VERSION = 3.0
 
 PROTOS = protobuf/vector_tile.proto
 include(protobuf/vector_tile.pri)