Allow reusing parser result across different searches.

[miensol]

The API exposed by the module does not allow to cache Parser.parse results to be reused across subsequent searches. One use case is to easily apply single projection over many json documents fetched as i.e. database rows using streaming API. Reusing the parse result would also result in performance improvement.

This pull request is a proposal of an API to achieve that:

const jmespath = require('jmespath');
const projection = jmespath.searcher('products[*].name');
const projectedRows = query().map(row => projection(row));