Add customQuery option

[THernandez03]

In some cases, the source url has another parameter name like q instead of query, so this commit adds customQuery to replace that name.

[fitiskin]

Thanks @THernandez03

This can be done with combine option in this way:

combine: ({ query }) => ({
  q: query
})

I have updated the readme and passed object with default params to combine function.

p.s. Better late than never %)