Document DISTRHO_PLUGIN_WANT_FULL_STATE (#135)

* Document DISTRHO_PLUGIN_WANT_FULL_STATE

* Tweak DISTRHO_PLUGIN_WANT_FULL_STATE summary

distrho/DistrhoInfo.hpp

@@ -543,6 +543,16 @@ START_NAMESPACE_DISTRHO
  */
 #define DISTRHO_PLUGIN_WANT_STATE 1
 
+/**
+   Wherever the plugin implements the full state API.
+   When this macro is enabled, the plugin must implement a new getState(const char* key) function, which the host calls when saving its session/project.
+   This is useful for plugins that have custom internal values not exposed to the host as key-value state pairs or parameters.
+   Most simple effects and synths will not need this.
+   @note this macro is automatically enabled if a plugin has programs and state, as the key-value state pairs need to be updated when the current program changes.
+   @see Plugin::getState(const char*)
+ */
+#define DISTRHO_PLUGIN_WANT_FULL_STATE 1
+
 /**
    Wherever the plugin wants time position information from the host.
    @see Plugin::getTimePosition()