feat(code): switch to typescript, mock zillow api calls, fix xml parser
All good!

This looks pretty good, thanks for the PR. Can I ask the impetus for the change to typescript, etc.? Thanks.
Richard
Hi @ralucas I'm a big fan of Typescript when it comes to developing applications at scale since it makes refactoring and bug detection a breeze!
I did this since Typescript is my preferred language over raw JavaScript since I may need to implement this soon myself, unless @konsumer does: https://github.com/ralucas/node-zillow/issues/13.
Here's another repo I converted to Typescript successfully: https://github.com/adumont/tplink-cloud-api/commit/36d05f5224a8765b03b39a8a93ddd9945a0a6986
Also, I'd like to add that if you know JavaScript, you almost already know typescript! Depending on the settings of the compiler and linter, it can be pretty lax with explicitly defining types (declarations, return values, function arguments, etc).