Add support for AudioUnit and LADSPA plugin formats

[eliot-akira]

I confirmed that it works for AudioUnit effects. Haven't tested AudioUnit instruments, nor LADSPA plugins on Linux.

As mentioned in issue #9, I'm not so familiar with C++ so the code could probably be written more efficiently. Any advice would be appreciated. 😉

[eliot-akira]

I had to use these constants to detect if each plugin format class is defined. I don't know if there's a cleaner way to do it.

[eliot-akira]

I found this method .endsWith() in JUCE::String class.

[backlit-studio]

This is the right approach I think, thanks a lot.

We should be able to clean this up a bit by pulling all of the macros and path checking into a private function that just returns an AudioUnitPluginFormat instance (the base class of LADSPAPluginFormat, AudioUnitPluginFormat and VST3PluginFormat)

something like

AudioUnitPluginFormat format = getPluginFormat(pluginPath)
formatAU.findAllTypesForFile(foundPlugins, pluginPath);
description = foundPlugins[0];
instance = formatAU.createInstanceFromDescription(*description, setup.sampleRate, setup.bufferSize);

where getPluginFormat is something like:

AudioPluginFormat getPluginFormat(const String &commandLine) {
  #if (JUCE_PLUGINHOST_LADSPA && JUCE_LINUX)
    if (pluginPath.endsWith(".so")) { return LADSPAPluginFormat();}
  #endif
  ...
}

Would you mind giving that shot?

Thanks again!