Adds Swift Package Manager support around the proj.h C API

Author: paulsolt-ofsw

.gitignore

@@ -23,6 +23,7 @@ build.local.sh
 /.vs*
 /*build*
 /nbproject
+/.swiftpm
 
 # Autotools
 autom4te.cache

Package.swift

@@ -0,0 +1,55 @@
+// swift-tools-version: 5.10
+
+import PackageDescription
+
+let package = Package(
+    name: "proj",
+    platforms: [
+        .iOS(.v13), .macOS(.v13)
+    ],
+    products: [
+        .library(
+            name: "proj",
+//             type: .static,
+            type: .dynamic,
+            targets: ["proj"]
+        ),
+    ],
+    targets: [
+        .target(
+            name: "proj",
+            path: "src",
+            exclude: [
+                "apps",
+                "tests",
+                "CMakeLists.txt",
+                "lib_proj.cmake",
+                "check_md5sum.cmake",
+                "generate_wkt_parser.cmake",
+                "general_doc.dox",
+                "wkt1_grammar.y",
+                "wkt2_grammar.y",
+            ],
+            resources: [
+//                .copy("../proj.db") // What is this?
+            ],
+            publicHeadersPath: ".", // The C header files are mixed with src files, we use a modulemap.module to load "proj.h"
+            cSettings: [
+//                .headerSearchPath("../include/proj"),
+//                .headerSearchPath("../include/proj/internal"),
+//                .headerSearchPath("../include/proj/internal/vendor/nlohmann"),
+            ],
+            cxxSettings: [
+                .headerSearchPath("../include"),
+                .headerSearchPath("../include/proj"),
+                .headerSearchPath("../include/proj/internal"),
+                .headerSearchPath("../include/proj/internal/vendor/nlohmann"),
+            ],
+            linkerSettings: [
+                .linkedLibrary("c++"),
+                .linkedLibrary("sqlite3"),
+            ]
+        )
+    ],
+    cxxLanguageStandard: .cxx17
+)

src/module.modulemap

@@ -0,0 +1,7 @@
+module proj {
+    // Include the header, but not as an `umbrella header "proj.h"`, since it doesn't include all headers in src folder
+    // The src directory has a C header API and the implementation is C++ under the hood.
+    header "proj.h"
+    
+    export *
+}