Opus BSD 3-clause license

The Praat source code contains a copy of the Opus software (see Acknowledgments). Here is the Opus license text:

`Copyright (c) 2001-2011 Xiph.Org, Skype Limited, Octasic,
` `Jean-Marc Valin, Timothy B. Terriberry,
` `CSIRO, Gregory Maxwell, Mark Borgerding,
` `Erik de Castro Lopo
` `
` `Redistribution and use in source and binary forms, with or without
` `modification, are permitted provided that the following conditions
` `are met:
` `
` `- Redistributions of source code must retain the above copyright
` `notice, this list of conditions and the following disclaimer.
` `
` `- Redistributions in binary form must reproduce the above copyright
` `notice, this list of conditions and the following disclaimer in the
` `documentation and/or other materials provided with the distribution.
` `
` `- Neither the name of Internet Society, IETF or IETF Trust, nor the
` `names of specific contributors may be used to endorse or promote
` `products derived from this software without specific prior written
` `permission.
` `
` `THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
` ```AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
` `LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
` `A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR
` `CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
` `EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
` `PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
` `PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
` `LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
` `NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
` `SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
` `
` `Opus is subject to the royalty-free patent licenses which are
` `specified at:
` `
` `Xiph.Org Foundation:
` `https://datatracker.ietf.org/ipr/1524/
` `
` `Microsoft Corporation:
` `https://datatracker.ietf.org/ipr/1914/
` `
` `Broadcom Corporation:
` `https://datatracker.ietf.org/ipr/1526/
`