Return ConventionalCommit content in public interface

[lewismiddleton]

When using this package, I found that the return type of the Parse method didn't give me access to any of the attributes on the ConventionalCommit object.

Minimal Reproducer

package main

import (
	"fmt"

	"github.com/leodido/go-conventionalcommits"
	"github.com/leodido/go-conventionalcommits/parser"
)

// Example from https://github.com/leodido/go-conventionalcommits/blob/2713df998a1596207af6090215be9cbe2fd651be/parser/example_test.go#L81
func main() {
	i := []byte(`fix: correct minor typos in code

see the issue [0] for details
on typos fixed.

[0]: https://issue

Reviewed-by: Z
Refs #133`)
	opts := []conventionalcommits.MachineOption{
		parser.WithTypes(conventionalcommits.TypesConventional),
	}
	m, _ := parser.NewMachine(opts...).Parse(i)

	// fmt.Printf("%+v", m)
	fmt.Println(m.Description)
}

When running with the code above, I get:

./main.go:27:16: m.Description undefined (type conventionalcommits.Message has no field or method Description)

If you comment out the line referencing the Description and dump the object you get:

&{Type:fix Description:correct minor typos in code Scope:<nil> Exclamation:false Body:0x140001181b8 Footers:map[refs:[133] reviewed-by:[Z]] TypeConfig:1}⏎                                                                                        

I think this is because the Parse method returns a Message object instead of a ConventionalCommit

Even though the attributes get specified in the object, the type system isn't aware that those properties are available.

I think the fix for this is changing the return types to be the more specific *conventionalcommits.ConventionalCommit. This shouldn't lose any functionality because the ConventionalCommit struct implements the Message interface (it took me a quick reference to how interfaces work to figure this out)