Add steps to update-major-version-tag workflow to: 
* Reset the major version tag on the local runner in case it's needed for subsequent workflow steps; and 
* Display details on the new major version tag to verify it points to the latest release.

Remove / comment out-of-date section re: `coveralls-api-result`, only available in `v1.x`. 

Please send any questions, suggestions or requests re: this sole output option to support@coveralls.io.

* Add coverage-reporter-platform input option to control which architecture-specific version of coverage-reporter is downloaded and run by the github-action. 
* Since this option is not available for MacOS or Windows, we deliver warning messages if the option is set, but continue processing with default behavior. 
* We have also stepped back from returning exit code 1 when coverage-reporter-version is set on MacOS and, instead, now deliver a warning message and allowing processing to proceed with the latest version installed by Homebrew. 
* We have also added tests for different values of coverage-reporter-platform.
* We've added logic to handle the introduction of new platform-specific filenames available in versions from v0.6.15 up and the different contents of coveralls-checksums.txt to be backwards compatible with versions <= v0.6.14.