Changes for version 0.15.0
- Added `version_string` class method and made use of it in the `validate_pgxn_meta` script.
- The command-line app now defaults to a file named `META.json` in the current directory if no file name is passed.
- Fixed installation in the `pgxn` client libexec directory so that it first creates the directory if it does not exist. This is to adjust to a change in `pgxn` 1.0, which does not create the directory by default.
- validate_pgxn_meta - Validate the structure of a PGXN META.json file
- PGXN::Meta::Validator - Validate PGXN distribution metadata structures