Integrate NatSpec info in the console

[iamdefinitelyahuman]

Overview

In the console it should be possible to access Natspec info about a contract function.

Specification

The repr of a function currently shows the signature:

>>> kyber.swapTokenToToken
<ContractTx 'swapTokenToToken(address src, uint256 srcAmount, address dest, uint256 minConversionRate)'>

There should be an info() (or natspec()?) method to get an expanded view of this data:

>>> kyber.swapTokenToToken.info()
swapTokenToToken(address src, uint256 srcAmount, address dest, uint256 minConversionRate)
@dev makes a trade between src and dest token and send dest tokens to msg sender
@param src Src token
@param srcAmount amount of src tokens
@param dest Destination token
@param minConversionRate The minimal conversion rate. If actual rate is lower trade is canceled.
@return amount of actual dest tokens

It may also be possible to use the NatSpec to give more meaningful exception messages when contract inputs are given improperly.