Make more use of convenience methods

FossilOrigin-Name: 89fbd7a1520ecb65809b4c1bd10006ce9bb3a662cb7e7804abaf85d1ee1da63a

src/Alias.m

@@ -1,6 +1,15 @@
 #import "Alias.h"
 
 @implementation Alias
++ (instancetype)aliasWithName:(OFString *)name
+                       action:(OFString *)action
+                    persisted:(bool)persisted;
+{
+	return [[self alloc] initWithName:name
+	                           action:action
+	                        persisted:persisted];
+}
+
 - (instancetype)initWithName:(OFString *)name
                       action:(OFString *)action
                    persisted:(bool)persisted