Add back standardOutput and standardError as deprecated renamed properties (#288)

Author: marcprux

Sources/Subprocess/IO/Output.swift

@@ -216,6 +216,12 @@ extension OutputProtocol where Self == FileDescriptorOutput {
         )
     }
 
+    // TODO: remove for 1.0
+    @available(*, deprecated, renamed: "currentStandardOutput")
+    public static var standardOutput: Self {
+        return currentStandardOutput
+    }
+
     /// Creates a subprocess output that writes to the current process's standard error.
     ///
     /// The file descriptor isn't closed afterwards.
@@ -225,6 +231,12 @@ extension OutputProtocol where Self == FileDescriptorOutput {
             closeAfterSpawningProcess: false
         )
     }
+
+    // TODO: remove for 1.0
+    @available(*, deprecated, renamed: "currentStandardError")
+    public static var standardError: Self {
+        return currentStandardError
+    }
 }
 
 extension OutputProtocol where Self == StringOutput<UTF8> {