Add support for pam_get_authtok and minor cleanups. This change adds the pam_get_authtok function for PAM modules, as well as performing a few cleanups: - Pattern match in a few more places. - Pull out string-copying into a function. - Format and run clippy. - Replace outdated PAM doc links with man7.org pages.

[package]
name = "pam-http"
version = "0.1.0"
authors = ["Anthony Nowell <anowell@gmail.com>"]

[lib]
name = "pam_http"
crate-type = ["cdylib"]

[dependencies]
pam-bindings = { path = "../pam/" }
reqwest = { version = "0.11.3", features = ["blocking"] }