nostrdb: add initial swift integration

nostrdb/NdbTagElem.swift

@@ -0,0 +1,29 @@
+//
+//  NdbTagElem.swift
+//  damus
+//
+//  Created by William Casarin on 2023-07-21.
+//
+
+import Foundation
+
+struct NdbTagElem {
+    private let note: UnsafeMutablePointer<ndb_note>
+    private let tag: UnsafeMutablePointer<ndb_tag>
+    let index: Int32
+
+    init(note: UnsafeMutablePointer<ndb_note>, tag: UnsafeMutablePointer<ndb_tag>, index: Int32) {
+        self.note = note
+        self.tag = tag
+        self.index = index
+    }
+
+    func matches_char(c: AsciiCharacter) -> Bool {
+        return ndb_tag_matches_char(note, tag, index, c.cchar) == 1
+    }
+
+    func string() -> String {
+        return String(cString: ndb_tag_str(note, tag, index), encoding: .utf8) ?? ""
+    }
+}
+