Pthread Text 2.1.0

This is a minor release of OBS Pthread Text.
Changes are as below.

• Notarized packages for macOS.
• Revised build scripts to commonalize with other plugins.

There is no functional change at all.

This is a major version release of OBS Pthread Text.
There is no much difference from the previous release 0.1.0 but documentation is ready. The major version is increased since the API is stable.