Some of the files in the Arduino core were missing the license headers.They contain code which is either copied from previous Arduino cores(which were already LGPL-2.1-or-later), or has been submitted to thisrepository where most of the code is clearly LGPL-2.1-or-later.  In anycase, all the contributors have either been directly employed by Arduinoor have signed the CLA.Add the missing LGPL-2.1-or-later headers to the files.

The CAN files had a non-standard license which does not match the otherfiles in the repository. This commit updates the license header tomatch that of the other files.All of the contributors to these files have either been employed byArduino or have signed the CLA.

Minor updates to the license headers to make them more consistent amongthe repository.

The files in the test/ folder had a copyright notice, but no licenseinformation. This commit adds the LGPL-2.1-or-later SPDX licenseidentifier to all these files.

All files in this repository are licensed under the GNU Lesser GeneralPublic License version 2.1. Make this obvious by including the LICENSEfile in the root of the repository.In addition to the above clause, some files may also be distributed underadditional license terms. See each individual file for details.

The codespell spellchecker tool is used to automatically detect commonly misspelled words in the files of this project.The misspelled words dictionary was expanded in the latest release of codespell. Some of the text in the projectcodebase happens to match against newly added entries, which caused codespell to produce a false misspelled worddetection.Since the code that produced the detection is correct and intended, the false positive is resolved by configuringcodespell to ignore the problematic word.

Fix spell check false positive by ignoring word

Use the LGPL 2.1 or later license on all files