Add unittest structure.

No tests, just everything to add tests later.

test/meson.build

@@ -0,0 +1,15 @@
+
+
+tests = [
+]
+
+
+gtest_dep = dependency('gtest', fallback: ['gtest', 'gtest_dep'])
+
+foreach test_name : tests
+    test_exe = executable(test_name, [test_name+'.cpp'],
+                          link_with : kiwixlib,
+                          dependencies : all_deps + [gtest_dep],
+                          build_rpath : '$ORIGIN')
+    test(test_name, test_exe)
+endforeach