ResourceFormatLoader and ResourceFormatSaver are meant to be overridden
to add support for different formats in ResourceLoader and ResourceSaver.
Those should be exposed as they can be overridden in plugins.
On the other hand, all predefined subclasses of those two base classes
are only meant to register support for new file and resource types, but
should not and cannot be used directly from script, so they should not
be exposed.
Also unexposed ResourceImporterOGGVorbis (and thus its base class
ResourceImporter) which are editor-only.
- EditorExportPlugin's _export_begin accepts all the arguments related
to the current export (is_debug, path, flags).
- EditorExportPlugin API is extended with methods allowing to configure
iOS export: add_ios_framework, add_ios_plist_content,
add_ios_linker_flags, add_ios_bundle_file.
- iOS export template now contains Godot as a static library so that
it can be linked with third-party Frameworks and GDNative static
libraries.
- Adds method to DirAccess for recursive copying of a directory.
- Fixes iOS export to work with Xcode 9 (released recently).
