silent setup

- silent install without prompt as it's expected when we install nvm-windows from a script
- silent uninstall
- fix a warning (Warning: Line 80, Column 10: [Hint] Variable 'Result' never used)

nvm.iss

@@ -77,7 +77,7 @@ end;
 var
   nodeInUse: string;
 
-function TakeControl(np: string; nv: string): string;
+procedure TakeControl(np: string; nv: string);
 var
   path: string;
 begin
@@ -147,21 +147,26 @@ begin
     Exec(ExpandConstant('{cmd}'), '/C node -v > "' + TmpResultFile + '"', '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
     LoadStringFromFile(TmpResultFile, stdout);
     NodeVersion := Trim(Ansi2String(stdout));
-    msg1 := MsgBox('Node '+NodeVersion+' is already installed. Do you want NVM to control this version?', mbConfirmation, MB_YESNO) = IDNO;
-    if msg1 then begin
-      msg2 := MsgBox('NVM cannot run in parallel with an existing Node.js installation. Node.js must be uninstalled before NVM can be installed, or you must allow NVM to control the existing installation. Do you want NVM to control node '+NodeVersion+'?', mbConfirmation, MB_YESNO) = IDYES;
-      if msg2 then begin
-        TakeControl(NodePath, NodeVersion);
+    if WizardSilent then begin
+      TakeControl(NodePath, NodeVersion);
+    end
+    else begin
+      msg1 := MsgBox('Node '+NodeVersion+' is already installed. Do you want NVM to control this version?', mbConfirmation, MB_YESNO) = IDNO;
+      if msg1 then begin
+        msg2 := MsgBox('NVM cannot run in parallel with an existing Node.js installation. Node.js must be uninstalled before NVM can be installed, or you must allow NVM to control the existing installation. Do you want NVM to control node '+NodeVersion+'?', mbConfirmation, MB_YESNO) = IDYES;
+        if msg2 then begin
+          TakeControl(NodePath, NodeVersion);
+        end;
+        if not msg2 then begin
+          DeleteFile(TmpResultFile);
+          WizardForm.Close;
+        end;
       end;
-      if not msg2 then begin
-        DeleteFile(TmpResultFile);
-        WizardForm.Close;
+      if not msg1 then
+      begin
+        TakeControl(NodePath, NodeVersion);
       end;
     end;
-    if not msg1 then
-    begin
-      TakeControl(NodePath, NodeVersion);
-    end;
   end;
 
   // Make sure the symlink directory doesn't exist
@@ -172,13 +177,18 @@ begin
       RemoveDir(SymlinkPage.Values[0]);
     end;
     if not dir1 then begin
-      msg3 := MsgBox(SymlinkPage.Values[0]+' will be overwritten and all contents will be lost. Do you want to proceed?', mbConfirmation, MB_OKCANCEL) = IDOK;
-      if msg3 then begin
+      if WizardSilent then begin
         RemoveDir(SymlinkPage.Values[0]);
-      end;
-      if not msg3 then begin
-        //RaiseException('The symlink cannot be created due to a conflict with the existing directory at '+SymlinkPage.Values[0]);
-        WizardForm.Close;
+      end
+      else begin
+        msg3 := MsgBox(SymlinkPage.Values[0]+' will be overwritten and all contents will be lost. Do you want to proceed?', mbConfirmation, MB_OKCANCEL) = IDOK;
+        if msg3 then begin
+          RemoveDir(SymlinkPage.Values[0]);
+        end;
+        if not msg3 then begin
+          //RaiseException('The symlink cannot be created due to a conflict with the existing directory at '+SymlinkPage.Values[0]);
+          WizardForm.Close;
+        end;
       end;
     end;
   end;
@@ -199,7 +209,9 @@ var
   path: string;
   nvm_symlink: string;
 begin
-  MsgBox('Removing NVM for Windows will remove the nvm command and all versions of node.js, including global npm modules.', mbInformation, MB_OK);
+  if not UninstallSilent then begin
+    MsgBox('Removing NVM for Windows will remove the nvm command and all versions of node.js, including global npm modules.', mbInformation, MB_OK);
+  end;
 
   // Remove the symlink
   RegQueryStringValue(HKEY_LOCAL_MACHINE,