need to simplify/unify/document connection establishment

[atsushieno]

I'm in the process of writing native-oriented client app now, and it is getting complicated to find out the right way to establish connection to service, namely how to set up shared memory buffers in the right order. Since it's been changing, it was definitely left undocumented which is not good at all. It has to be changed.

[atsushieno]

Expected outcome:

• How-to documentation on query plugin services, bind service, instantiate plugin, prepare buffers, activate, process, deactivate, terminate, and unbind service. Some native parts are already summarized on README.
• documenting them means we will have the relevant API parts sorted out.

[atsushieno]

Worked on some API simplification, namely, removal of SharedMemoryExtension from public native API surface, is done in r0.6.22.

[atsushieno]

I'm done with aap-juce adoption too (both plugin and hosting). Now that it is only about the public plugin API matter (libandroidaudioplugin is not public), I can close this particular issue.