Add proc macro package for automatic IndexList<T> implementation

[y-pakorn]

This will resolve #736

macro crate feature on cw-storage-plus is not enabled by default.

cw-storage-macro doesn't need to be published into crate.io because the macro is re-exported in cw-storage-plus package.

#[derive(Serialize, Deserialize, Clone, Debug, PartialEq, JsonSchema)]
pub struct Token {
  pub owner: Addr,
  pub ticker: String,
  pub identifier: u8,
}

#[index_list(Token)]
pub struct TokenIndexes<'a> {
  pub identifier: UniqueIndex<'a, U8Key, Token>,
}

[CLAassistant]

All committers have signed the CLA.

[maurolacy]

Thanks for your contribution.

LTGM. Just some docs / comments style suggestions.

[maurolacy]

Seems the code coverage tool is being confused by the macro. We need to solve that before merging.

[y-pakorn]

Seems the code coverage tool is being confused by the macro. We need to solve that before merging.

Might we need an additional tarpaulin config flag to cover integration tests?

[maurolacy]

Seems the code coverage tool is being confused by the macro. We need to solve that before merging.

Might we need an additional tarpaulin config flag to cover integration tests?

Not sure how to address this. Also, please add the new storage-macro package to the README.md, under Utilities.

[maurolacy]

Seems the code coverage tool is being confused by the macro. We need to solve that before merging.

Might we need an additional tarpaulin config flag to cover integration tests?

Not sure how to address this. Also, please add the new storage-macro package to the README.md, under Utilities.

This is just because this is a new package, that doesn't have previous runs.

Merging now. Adding to README is not needed, because this is a private package.