Adds v0.3.0 files to v0 module (#20)

[TanmoySG]

This PR reinstates v0 of the GoStep library within the v0 sub module, to ensure backwards compatibility.

• Closes Support for v0 #20

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This pull request introduces significant changes to the go-steps library, including updates to the documentation and the addition of new examples, functions, and types for better functionality and error handling. The most important changes include updates to the README.md, new examples demonstrating the use of the library, and the introduction of new types and constants.

Documentation Updates:

• README.md: Updated the note about breaking changes in go-steps v1 and provided guidance on how to continue using v0. Removed the "Help" section. [1] [2]

New Examples:

• example/v0/dynamic-steps-example/main.go: Added a new example demonstrating dynamic step chaining and execution.
• example/v0/multistep-example/main.go: Added a new example demonstrating multi-step execution with conditional next steps and error handling.

New Functions and Types:

• v0/go_step_types.go: Introduced new types (StepName, StepFn, PossibleNextSteps, Step, stepArgChainingType) to define steps and their configurations.
• v0/go_steps_constants.go: Added constants and variables for default and maximum step attempts, and argument chaining types.

Step Execution and Error Handling:

• v0/go_steps.go: Implemented the Execute method for the Step type, including logic for step execution, argument resolution, and error handling with retries.
• v0/go_steps_errors.go: Added error messages for unresolved steps.

Testing:

• v0/go_steps_test.go: Added tests for step argument resolution, next step resolution, and retry logic.