Migrate to new spec (partiql#106)

Migrated tests from old spec to PTS spec

Also fixes a multiple PTS bugs and integrates it with the ref implementation

* set_default_environment can be a file path or a struct with the
environment
* equality for struct elements were using Ion equality instead of PTS
equality
* Interpolation now accepts both $variable or ${variable} when
interpolating strings
* using absolute path for test files in errors for better error
reporting
* JUnitRunner generated name now includes the test location location along with
the test id