Create methods dynamically

[bonustrack]

Blocked by #9

Based on the file created from #9, we should create function from steemd API dynamically. The goal is to allow this kind of possibility with lightrpc:

// with callback
client.getAccounts(['fabien'], (err, result) => {});

// with promise
client.getAccounts(['fabien']).then(result => {}); 

// with named params
client.getAccounts({ names: ['fabien'] }, (err, result) => {}); 

// with named params and promise
client.getAccounts({ names: ['fabien'] }).then(result => {});

// empty param should display description of the method
client.getAccounts();