*/bats-*: rename and new aports & take over maintainership

1. rename main/bats to main/bats-core (following upstream) & take over maintainership
2. new aport: bats-{file, support, assert}
3. new meta package bats for bats-{core, file, support, assert}

update: take over maintainership

I emailed previous maintainer on August 15th but haven't received a reply until now.

upstream:

• https://github.com/bats-core/bats-assert
• https://github.com/bats-core/bats-support
• https://github.com/bats-core/bats-core
• https://github.com/bats-core/bats-file