Add methods descriptions to ABI JSON

[cusma]

Currently the Smart ASA ABI JSON, automatically generated by PyTeal, does not include methods descriptions.

Would be very useful to improve the JSON ABI once this improvement is merged into PyTeal.

Example:

def asset_transfer(
    xfer_asset: abi.Asset,
    asset_amount: abi.Uint64,
    asset_sender: abi.Account,
    asset_receiver: abi.Account,
) -> Expr:
    """
    Smart ASA Transfer: regular, mint, burn, clawback.
    
    Args:
        xfer_asset: Smart ASA ID.
        asset_amount: Smart ASA amount.
        asset_sender: Account to transfer Smart ASA from.
        asset_receiver: Account to transfer Smart ASA to.
    """
    ...