Adding support for POST method

This adds support for POST method when the property "method" is defined in the JSON file and its value is "POST".

Example:
{
	"url" : "http://example.com",
	"method": "POST",
	"collections" : [{
		"name" : "data",
		"query": "$('tr > td:first-child')",
		"fields": {
			"time" : "text()"
		}
	}]
}