Improve version.pri.

Now you can set a version number only in one place.

version.pri

@@ -1,5 +1,25 @@
-PROJECT_NAME = qbittorrent
-PROJECT_VERSION = 3.2.0alpha
+PROJECT_NAME = qBittorrent
+
+# Define version numbers here
+VER_MAJOR = 3
+VER_MINOR = 2
+VER_BUGFIX = 0
+VER_BUILD = 0
+VER_STATUS = alpha # Should be empty for stable releases!
+
+# Don't touch the rest part
+PROJECT_VERSION = $${VER_MAJOR}.$${VER_MINOR}.$${VER_BUGFIX}
+
+!equals(VER_BUILD, 0) {
+    PROJECT_VERSION = $${PROJECT_VERSION}.$${VER_BUILD}
+}
+
+PROJECT_VERSION = $${PROJECT_VERSION}$${VER_STATUS}
+
+DEFINES += VERSION_MAJOR=$${VER_MAJOR}
+DEFINES += VERSION_MINOR=$${VER_MINOR}
+DEFINES += VERSION_BUGFIX=$${VER_BUGFIX}
+DEFINES += VERSION_BUILD=$${VER_BUILD}
 
 os2 {
     DEFINES += VERSION=\'\"v$${PROJECT_VERSION}\"\'
@@ -7,6 +27,3 @@ os2 {
     DEFINES += VERSION=\\\"v$${PROJECT_VERSION}\\\"
 }
 
-DEFINES += VERSION_MAJOR=3
-DEFINES += VERSION_MINOR=2
-DEFINES += VERSION_BUGFIX=0