add project scope and release plan files

add LICENSE and NOTICE files

- tailor README for asciidoc-lang
- move LICENCE file into docs
- change Antora component name from "asciidoc" to "docs"
- remove placeholder CHANGELOG file at root
- add Antora playbook for building documentation locally

resolves #51 document the normalization applied to the AsciiDoc source and AsciiDoc include files (PR #52)

Authored by: David Jencks <djencks@apache.org>

add additional example for tag filtering for including lines outside of tags and inside a specified tag

* rewrite much of the description of link attribute parsing to reflect the simplified parsing behavior implemented in https://github.com/asciidoctor/asciidoctor/issues/2059
* remove the detail about how positional attributes are parsed, which will be covered in a dedicated page

Authored by: David Jencks <djencks@apache.org>

Authored by: Younes-L <Younes-L@users.noreply.github.com>

Authored by: David Jencks <djencks@apache.org>

"You can solve this probably" -> "You can solve this problem"

Authored by: Duncan Lock <duncan.lock@gmail.com>