Fix incorrect usage of shared_module in extensions
Meson 0.60.2 prints the following warnings:
DEPRECATION: target exiv2_tools links against shared module edit_metadata, which is incorrect.
This will be an error in the future, so please use shared_library() for edit_metadata instead.
If shared_module() was used for edit_metadata because it has references to undefined symbols,
use shared_libary() with `override_options: ['b_lundef=false']` instead
This somehow causes that created libimporter.so doesn't have SONAME and extensions linked with libimporter.so has the following entry in ELF header:
0x0000000000000001 (NEEDED) Shared library: [extensions/importer/libimporter.so]
This is wrong, there should be just libimporter.so (as in all other extension libs), not extensions/importer/libimporter.so.
Fixes #204 (closed)