provider(AUR): Add AUR as a provider

Cargo.toml

README.md

mastersearch-all/Cargo.toml

mastersearch-all/src/lib.rs

mastersearch-aur/Cargo.toml

mastersearch-aur/README.md

mastersearch-aur/examples/search.rs

mastersearch-aur/src/api/mod.rs

mastersearch-aur/src/api/structure.rs

mastersearch-aur/src/lib.rs