AWIS batch requests and special character handling

This enables batch requests of up to 5 queries as specified in the AWIS documentation by alternatively providing a list of URLs. Example:

tree = api.url_info(("example1.com", "example2.com", "example3.com"), "Rank", "LinksInCount")

Providing a string as first argument still works:

tree = api.url_info("example.com", "Rank", "LinksInCount")

Note that requests submitted in batch are still billed separately by AWS, so this only saves time not money.

This also fixes an issue with retrieving information on URLs containing a tilde character by additional escaping.