Add support for dynamic partials

Sources/HummingbirdMustache/Template+Render.swift

@@ -8,7 +8,11 @@ extension HBMustacheTemplate {
                 string += text
             case .variable(let variable):
                 if let child = getChild(named: variable, from: object) {
-                    string += encodedEscapedCharacters(String(describing: child))
+                    if let template = child as? HBMustacheTemplate {
+                        string += template.render(object, library: library)
+                    } else {
+                        string += encodedEscapedCharacters(String(describing: child))
+                    }
                 }
             case .unescapedVariable(let variable):
                 if let child = getChild(named: variable, from: object) {

Tests/HummingbirdMustacheTests/TemplateRendererTests.swift

@@ -192,6 +192,7 @@ final class TemplateRendererTests: XCTestCase {
             """)
     }
     
+    /// Testing partials
     func testMustacheManualExample9() throws {
         let library = HBMustacheLibrary()
         let template = try HBMustacheTemplate(string: """
@@ -215,4 +216,28 @@ final class TemplateRendererTests: XCTestCase {
 
             """)
     }
+
+    /// Testing dynamic partials
+    func testDynamicPartials() throws {
+        let library = HBMustacheLibrary()
+        let template = try HBMustacheTemplate(string: """
+            <h2>Names</h2>
+            {{partial}}
+            """)
+        let template2 = try HBMustacheTemplate(string: """
+            {{#names}}
+              <strong>{{.}}</strong>
+            {{/names}}
+            """)
+        library.register(template, named: "base")
+        
+        let object: [String: Any] = ["names": ["john", "adam", "claire"], "partial": template2]
+        XCTAssertEqual(library.render(object, withTemplateNamed: "base"), """
+            <h2>Names</h2>
+              <strong>john</strong>
+              <strong>adam</strong>
+              <strong>claire</strong>
+
+            """)
+    }
 }