Support HTTP methods

[ridhoq]

Adds optional argument for HTTP method. If one isn't passed, GET is used by default.

af POST https://google.com <-- POST google.com
af https://google.com <-- GET google.com

I had a lot of issues trying to support this optional argument. The author of ht opened this issue: clap-rs/clap#2122 which shows what I was trying to do. They ended up working around it as seen here. For now, I decided to use AllowMissingPositional, but we'll see if that changes.

However, there is a bug when using AllowMissingPositional (clap-rs/clap#1737) causes my usage message to look like this:

af 0.0.3
A (http) fetch CLI 😀👍

USAGE:
    af <URI> [METHOD]

FLAGS:
    -h, --help       Prints help information
    -V, --version    Prints version information

ARGS:
    <METHOD>    HTTP method. If no HTTP method is provided, GET is used by default [default: GET]
    <URI>       URI to fetch

The URI and METHOD args are swapped 🤦🏽 I'm prolly gonna have to hack around this somehow or take a stab at fixing it upstream.

Closes #1