doc: mention plugin interface string in plugin interface docs.

src/Magnum/Audio/AbstractImporter.h

@@ -59,6 +59,8 @@ checked by the implementation:
     supported.
 -   All `do*()` implementations working on opened file are called only if
     there is any file opened.
+
+Plugin interface string is `"cz.mosra.magnum.Audio.AbstractImporter/0.1"`.
 */
 class MAGNUM_AUDIO_EXPORT AbstractImporter: public PluginManager::AbstractPlugin {
     CORRADE_PLUGIN_INTERFACE("cz.mosra.magnum.Audio.AbstractImporter/0.1")

src/Magnum/Text/AbstractFont.h

@@ -71,6 +71,8 @@ checked by the implementation:
     @ref Feature::OpenData is supported.
 -   All `do*()` implementations working on opened file are called only if
     there is any file opened.
+
+Plugin interface string is `"cz.mosra.magnum.Text.AbstractFont/0.2.3"`.
 */
 class MAGNUM_TEXT_EXPORT AbstractFont: public PluginManager::AbstractPlugin {
     CORRADE_PLUGIN_INTERFACE("cz.mosra.magnum.Text.AbstractFont/0.2.3")

src/Magnum/Text/AbstractFontConverter.h

@@ -67,6 +67,8 @@ checked by the implementation:
     if @ref Feature::ConvertData is supported.
 -   Function `doImport*FromData()` is called only if there is at least one data
     array passed.
+
+Plugin interface string is `"cz.mosra.magnum.Text.AbstractFontConverter/0.1.1"`.
 */
 class MAGNUM_TEXT_EXPORT AbstractFontConverter: public PluginManager::AbstractPlugin {
     CORRADE_PLUGIN_INTERFACE("cz.mosra.magnum.Text.AbstractFontConverter/0.1.1")

src/Magnum/Trade/AbstractImageConverter.h

@@ -55,6 +55,8 @@ checked by the implementation:
 
 -   Functions @ref doExportToImage() or @ref doExportToData() are called only
     if @ref Feature::ConvertImage or @ref Feature::ConvertData is supported.
+
+Plugin interface string is `"cz.mosra.magnum.Trade.AbstractImageConverter/0.2.1"`.
 */
 class MAGNUM_EXPORT AbstractImageConverter: public PluginManager::AbstractPlugin {
     CORRADE_PLUGIN_INTERFACE("cz.mosra.magnum.Trade.AbstractImageConverter/0.2.1")

src/Magnum/Trade/AbstractImporter.h

@@ -72,6 +72,8 @@ checked by the implementation:
 -   All `do*()` implementations taking data ID as parameter are called only if
     the ID is from valid range.
 
+Plugin interface string is `"cz.mosra.magnum.Trade.AbstractImporter/0.3"`.
+
 @todo How to handle casting from std::unique_ptr<> in more convenient way?
 */
 class MAGNUM_EXPORT AbstractImporter: public PluginManager::AbstractManagingPlugin<AbstractImporter> {
@@ -94,7 +96,7 @@ class MAGNUM_EXPORT AbstractImporter: public PluginManager::AbstractManagingPlug
         /** @brief Default constructor */
         explicit AbstractImporter();
 
-        /** @brief Default constructor with access to plugin manager */
+        /** @brief Constructor with access to plugin manager */
         explicit AbstractImporter(PluginManager::Manager<AbstractImporter>& manager);
 
         /** @brief Plugin manager constructor */