Add object style for calling iost.transfer

[nujabes403]

Calling transfer like const tx = iost.transfer(tokenSym, accountList[0].getID(), "admin", "55.000000001"); sometimes verbose.

I added object-style calling method for it.

After this PR it can be possible to call like below:

iost.transfer({
  token: 'iost',
  from: '...',
  to: '...',
  amount: '...',
  memo: '...',
})

I think the above one is more friendly from ethereum-experienced developers.
How do you think about it? Please check it :)