Autogenerate abi/metadata package (#58)

* Use into for constructing toml values

* Promote workspace mod to directory

* Fix import warnings

* Update license headers

* Remove abi package from template, generate it instead

* Extract contract name and generate files

* Fix some errors

* Insert ink_lang dependency

* Fmt

* ink! v2 compatibility

* Use new generate_metadata extern

* Warn the user if they have legacy abi_gen artifacts

* Move existing abi package check to the right place

* Remove v2 backwards compat, use ink! master in template

* Remove type_metadata dependency

* Fix up template for working with ink! master

* Update template lib.rs for ink! 3

* Fix template

* Fix template constructors

* Try again with template

* Move template files to templates dir

* Rename abi to metadata

* Rename abi constant and update warning

* More renames from abi to metadata

* Document generate_package function

* Fmt

* More abi to metadata renames

* Update template parity-scale-codec

* Bump version