Full support for axios replacement (haxios ;-))

[simllll]

Is your feature request related to a problem? Please describe.
Right now it's not possible to use gaxois as a drop-in replacmenet for axios, as there are some core things missing:

• get, post, etc helper methods are not available
• there is no built-in support for interceptors
• not all config options are supported

Describe the solution you'd like
Allow an (almost) identical API of current axios, to allow gaxios as an 1:1 replacement.

I added the missing functionality in "haxios" which is based on gaxios: https://github.com/hokify/haxios

My question now is: are you interested in bringing this into gaxios? Or is this by design not supported? If so ,what are the reasoning for it? If not, how can I help to make this happening? :)