Currently we use quite a lot of different formatting for license types and copyright holders, and while it is not really important for a hobby project, such as ours, I believe it is reasonable to update things for simplicity and to reduce the bureaucracy.

From there on I request us to use BSD-3-Clause everywhere as before with the following formatting for file headers.

Notes:

• I am not positive whether to use <BR> between copyright holders, as in my opinion it reduces readability, but may be required by doxygen.
• I am not sure about additional description, most likely it should go after SPDX-License-Identifier separated by an empty line.
• I am not positive whether we want more empty lines.

C-like languages:

/** @file
  Copyright (c) 2015-2019, vit9696. All rights reserved.
  Copyright (c) 2016, Download-Fritz. All rights reserved.
  Copyright (c) 2019, SomeOtherPerson. All rights reserved.
  SPDX-License-Identifier: BSD-3-Clause
**/

or

/** @file
  Super duper protocol implementation on XYZ firmware.

  Copyright (c) 2015-2019, vit9696. All rights reserved.
  Copyright (c) 2016, Download-Fritz. All rights reserved.
  Copyright (c) 2019, SomeOtherPerson. All rights reserved.
  SPDX-License-Identifier: BSD-3-Clause
**/

inf/python/perl:

## @file
# Copyright (c) 2015-2019, vit9696. All rights reserved.
# SPDX-License-Identifier: BSD-3-Clause
##

or

## @file
# Super duper protocol implementation on XYZ firmware.
#
# Copyright (c) 2015-2019, vit9696. All rights reserved.
# SPDX-License-Identifier: BSD-3-Clause
##

nasm:

;------------------------------------------------------------------------------
; @file
; Copyright (c) 2015-2019, vit9696. All rights reserved.
; SPDX-License-Identifier: BSD-3-Clause
;------------------------------------------------------------------------------

or

;------------------------------------------------------------------------------
; @file
; Super duper protocol implementation on XYZ firmware.
;
; Copyright (c) 2015-2019, vit9696. All rights reserved.
; SPDX-License-Identifier: BSD-3-Clause
;------------------------------------------------------------------------------