Add memo field in transfer functions

It would be nice to add a `memo` field to the `stx_transferSip10Ft` and `stx_transferSip09Nft` request functions.

```
let response = await request('stx_transferSip10Ft', {
    asset: "SM3VDXK3WZZSA84XXFKAFAF15NNZX32CTSG82JFQ4.sbtc-token::sbtc-token",
    amount: amount.value,
    recipient: 'SP1HEJ1XHBJZJFNA2AECYQXQGZD8EQE4F30D6H5CR',
    memo?: "some memo"
  })
```