Optimized size

Removed Ajax functions:

• Remove ajax(). Since the DOM API fetch() is almost the same (it's better actually!) and the awesome https://polyfill.io/ already covers for older browsers, ajax() is totally pointless nowadays.
• Remove the method .ajax(), this is a small helper that I have never ever used and is strongly tied to the former.

In exchange of these, the library decreased from 3.5kb to 2.5kb, an almost 30% decrease in size. Tiny enough to embed it anywhere easily.

See migration guide and original issue.