Modify font descriptor traits when applying bold/italic formatting

instead of replacing font entirely.

Fixes #51

Tusker.xcodeproj/project.pbxproj

@@ -118,6 +118,7 @@
 		D667E5F12134D5050057A976 /* UIViewController+Delegates.swift in Sources */ = {isa = PBXBuildFile; fileRef = D667E5F02134D5050057A976 /* UIViewController+Delegates.swift */; };
 		D667E5F52135BCD50057A976 /* ConversationTableViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = D667E5F42135BCD50057A976 /* ConversationTableViewController.swift */; };
 		D667E5F82135C3040057A976 /* Mastodon+Equatable.swift in Sources */ = {isa = PBXBuildFile; fileRef = D667E5F72135C3040057A976 /* Mastodon+Equatable.swift */; };
+		D66A77BB233838DC0058F1EC /* UIFont+Traits.swift in Sources */ = {isa = PBXBuildFile; fileRef = D66A77BA233838DC0058F1EC /* UIFont+Traits.swift */; };
 		D6757A7C2157E01900721E32 /* XCBManager.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6757A7B2157E01900721E32 /* XCBManager.swift */; };
 		D6757A7E2157E02600721E32 /* XCBRequestSpec.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6757A7D2157E02600721E32 /* XCBRequestSpec.swift */; };
 		D6757A822157E8FA00721E32 /* XCBSession.swift in Sources */ = {isa = PBXBuildFile; fileRef = D6757A812157E8FA00721E32 /* XCBSession.swift */; };
@@ -376,6 +377,7 @@
 		D667E5F02134D5050057A976 /* UIViewController+Delegates.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "UIViewController+Delegates.swift"; sourceTree = "<group>"; };
 		D667E5F42135BCD50057A976 /* ConversationTableViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ConversationTableViewController.swift; sourceTree = "<group>"; };
 		D667E5F72135C3040057A976 /* Mastodon+Equatable.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "Mastodon+Equatable.swift"; sourceTree = "<group>"; };
+		D66A77BA233838DC0058F1EC /* UIFont+Traits.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "UIFont+Traits.swift"; sourceTree = "<group>"; };
 		D6757A7B2157E01900721E32 /* XCBManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = XCBManager.swift; sourceTree = "<group>"; };
 		D6757A7D2157E02600721E32 /* XCBRequestSpec.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = XCBRequestSpec.swift; sourceTree = "<group>"; };
 		D6757A812157E8FA00721E32 /* XCBSession.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = XCBSession.swift; sourceTree = "<group>"; };
@@ -893,6 +895,7 @@
 				D6333B782139AEFD00CE884A /* Date+TimeAgo.swift */,
 				D67C57AE21E28EAD00C3118B /* Array+Uniques.swift */,
 				0450531E22B0097E00100BA2 /* Timline+UI.swift */,
+				D66A77BA233838DC0058F1EC /* UIFont+Traits.swift */,
 			);
 			path = Extensions;
 			sourceTree = "<group>";
@@ -1559,6 +1562,7 @@
 				D6D58DF922074B74009C8DD9 /* LinkLabel.swift in Sources */,
 				0454DDAF22B462EF00B8BB8E /* GalleryExpandAnimationController.swift in Sources */,
 				D6A3BC8A2321F79B00FD64D5 /* AccountTableViewCell.swift in Sources */,
+				D66A77BB233838DC0058F1EC /* UIFont+Traits.swift in Sources */,
 				D68FEC4F232C5BC300C84F23 /* SegmentedPageViewController.swift in Sources */,
 				0450531F22B0097E00100BA2 /* Timline+UI.swift in Sources */,
 				D667E5F52135BCD50057A976 /* ConversationTableViewController.swift in Sources */,

Tusker/Extensions/UIFont+Traits.swift

@@ -0,0 +1,21 @@
+//
+//  UIFont+Traits.swift
+//  Tusker
+//
+//  Created by Shadowfacts on 9/22/19.
+//  Copyright © 2019 Shadowfacts. All rights reserved.
+//
+
+import UIKit
+
+extension UIFont {
+    
+    func addingTraits(_ traits: UIFontDescriptor.SymbolicTraits, size: CGFloat? = nil) -> UIFont? {
+        let descriptor = self.fontDescriptor
+        guard let newDescriptor = descriptor.withSymbolicTraits([descriptor.symbolicTraits, traits]) else {
+            return nil
+        }
+        return UIFont(descriptor: newDescriptor, size: size ?? self.pointSize)
+    }
+    
+}

Tusker/Views/ContentLabel.swift

@@ -128,9 +128,11 @@ class ContentLabel: LinkLabel {
             case "p":
                 attributed.append(NSAttributedString(string: "\n\n"))
             case "em", "i":
-                attributed.addAttribute(.font, value: UIFont.italicSystemFont(ofSize: font!.pointSize), range: attributed.fullRange)
+                let currentFont: UIFont = attributed.attribute(.font, at: 0, effectiveRange: nil) as? UIFont ?? self.font
+                attributed.addAttribute(.font, value: currentFont.addingTraits(.traitItalic), range: attributed.fullRange)
             case "strong", "b":
-                attributed.addAttribute(.font, value: UIFont.boldSystemFont(ofSize: font!.pointSize), range: attributed.fullRange)
+                let currentFont: UIFont = attributed.attribute(.font, at: 0, effectiveRange: nil) as? UIFont ?? self.font
+                attributed.addAttribute(.font, value: currentFont.addingTraits(.traitBold), range: attributed.fullRange)
             case "del":
                 attributed.addAttribute(.strikethroughStyle, value: NSUnderlineStyle.single.rawValue, range: attributed.fullRange)
             case "code":