Suggest upcoming change to macro syntax

[soumyamahunt]

I am recently redesigning public API along with making the macro implementation modular in #12. This will replace current @CodablePath and @CodableCompose with @CodedAt and @CodedIn macros. There will be no reduction in functionality provided by this library, and existing functionality can be preserved by doing following modifications:

• Replace @CodableCompose usage with @CodedAt macro without any path arguments.
• Replace @CodablePath usage with path arguments with @CodedAt macro with the same path arguments.
• Replace @CodablePath usage without path arguments with @CodedIn macro without any path arguments.

Currently you can specify default value and custom serializer with default and helper arguments respectively. This makes the macro syntax heavy over the variable declaration. I am thinking of breaking these functionalities into separate macros, i.e.

• default argument will be removed and replaced with @Default macro.
• helper argument will be removed and replaced with @CodedBy macro.

The current syntax:

@CodedAt("key", default: ["some"], helper: LossySequenceCoder())
let value: [String]

can be transformed to:

@CodedBy(LossySequenceCoder())
@Default(["some"])
@CodedAt("key")
let value: [String]

[soumyamahunt]

Implementation for this added in #14.