fetcher-core crate

[nachog00]

• Initialised cargo-fetcehr crate
• initialised file structure
• new error.rs module
• new cache.rs module
• new binaries module
• new binaries module
• updated fetcher-core lib.rs
• format cargo.toml
• new get_path function in cache
• new error "InvalidResource"
• remove binary_cofig module not nieeded anymore after next refactor
• .
• removed unnecesary implementations of ResourceType
• implemented correct Resource trait
• implemented Resource for Binaries
• updated public api to use latest Resource implementation
• added tokio as a dep of fetcher-core
• more logging
• implemented get_name as Resource for Binaries
• fix: &Cache for get_path
• removed unnecesary 'get' fn and implemented dummy fn's for Binaries's Resource trait
• updated get_result 's types
• added assert!(false) in dummy function to see outpu on fail

[nachog00]

This PR aims to implement the functionality outlined in #31

As of now, it provides a base structure for serving arbitrary resources.

The old fetcher logic can already be ported in.

[nachog00]

Merging this into feature branch fetcher-core_crate.

New PR's can be open against this branch to elaborate on the fetcher-core feature until it is ready to land in dev.