BC: redesign for PURL 1.0

[jkowalleck]

PackageURL 1.0 was releqsed - https://github.com/package-url/purl-spec/releases/tag/v1.0.0 🎉

with this, we can finally rework the whole implementation to adhere the final Spec.

blockers

Unfortunately, the spec is not entire explicit, the actual grammar is not part of the spec, yet
Implementing the implicit rules of the spec is error-prone, relying on non-spec rules like how-to-build.md and how-to-parse.md is kind of a "best-effort" implementation. Therefore:

• waiting for spec: add grammar (ABNF) purl-spec#578

expected outcome

• have a namespace PackageUrl\Core - everything defined in the STANDARD and in additionalmaterial
  • data models and enums andconstants - https://github.com/package-url/purl-spec/blob/main/docs/known-qualifiers.md
  • parsers - https://github.com/package-url/purl-spec/blob/main/docs/how-to-parse.md
  • stringifiers and canonicalizers - https://github.com/package-url/purl-spec/blob/main/docs/how-to-build.md
• have a namespace PackageUrl\Types - for implementations related to specific types
  • empty at first
  • add an example implementation for composer - https://github.com/package-url/purl-spec/blob/main/types-doc/composer-definition.md
• have a namespace PackageUrl\Contrib - for everything not defined in the standard
  • empty at first

have tests for the core implementation and the implanted type(s) -
shall use the tests provided by https://github.com/package-url/purl-spec/tree/main/tests

have the README tell about the different sub-namespaces and their purposes.

[jkowalleck]

⚠️ ⚠️ ⚠️ ⚠️

the actual design is not clear and shall be discussed here.

[jkowalleck]

regarding parsing and validating:
as soon as the grammar (package-url/purl-spec#578) is done, we might implement it.

take an inspiration on how SPDX lib does this: https://github.com/composer/spdx-licenses/blob/5ecd0cb4177696f9fd48f1605dda81db3dee7889/src/SpdxLicenses.php#L305-L343

translating the grammar to regex, instead of using a slow ABNF parser-generator might speed things up and causes no additional dependencies.