Merge compilesdk= into target=, better documentation about target=

docs/fdroid.texi

@@ -836,22 +836,17 @@ is sdk-location. Typically, if you get a message along the lines of:
 try enabling this option.
 
 @item target=<target>
-Specifies a particular SDK target for compilation, overriding the
-project.properties of the app and possibly sub-projects. Note that this does
-not change the target SDK in the AndroidManifest.xml — the level of features
-that can be included in the build. This is likely to cause the whole build.xml
-to be rewritten, which is fine if it's a 'standard' android file or doesn't
-already exist, but not a good idea if it's heavily customised. If you get an
-error about invalid target, first try @code{init=rm -rf bin/}; otherwise this
-parameter should do the trick.
+Specifies a particular SDK target for compilation, overriding the value
+defined in the code by upstream.  This has different effects depending on what
+build system used — this flag currently affects ant, maven and gradle projects
+only. Note that this does not change the target SDK in the
+AndroidManifest.xml, which determines the level of features that can be
+included in the build.
 
-Please note that gradle builds should be using compilesdk=.
-
-@item compilesdk=<level>
-Practically accomplishes the same that target= does when used in ant and maven
-projects. compilesdk= is used rather than target= so as to not cause any more
-confusion. It only takes effect on gradle builds in the build.gradle file,
-thus using it in any other case is not wise.
+In the case of an ant project, it modifies project.properties of the app and
+possibly sub-projects. This is likely to cause the whole build.xml to be
+rewritten, which is fine if it's a 'standard' android file or doesn't already
+exist, but not a good idea if it's heavily customised.
 
 @item update=xxx
 By default, 'android update project' is used to generate or update the