add query builder

[vsimko]

In select function the parameters for solr are now passed as an object, e.g. as follow:

const solr = require('node-solr-lambda').prepareSolrClient()
const results = await solr.select({
  q: 'label:test',
  sort: 'label desc',
  core: 'my_core'
})

It would be nice to have a builder function that creates the parameters in a more convenient way. For example by making use of intellisense in vscode:

const {prepareSolrClient, query} = require('node-solr-lambda')
const solr = prepareSolrClient()
const params = query('label:test').sort('label').desc()
const results = await solr.select(params, 'my_core')

[vsimko]

I decided not to do it because I think that the current implementation is much better and closer to the actual solr API. The vscode IDE uses our typescript type definitions to provide intellisense assistance.
The type information is only needed at design time and irrelevant to the runtime.
This way, we can happily code in plain javascript while leveraging optional type checking from typescript.