Fix method for "get", "post", "put", "patch" and "del" request creators

[StefanoMagrassi]

Description

Currently the main module (src/index.ts) exposes 5 request creators with method already set (get, post, put, patch and del) using an internal combinator (setMethod).

This combinator suffers of the same bug of #328: the method wont be overwritten by subsequent combinators or provided RequestInit.

Current behavior

appy.post(['http://some.endpoint'], {method: 'GET'}) ignores method in RequestInit always sending request as POST

Expected behavior

appy.post(['http://some.endpoint'], {method: 'GET'}) should send request as GET

Environment:

• OS: all
• Browser: all
• Node/npm version: all
• Typescript version: all

Additional information

We can take advantage of this fix to expose a new combinator withMethod that can be used by the lib's consumers.