Move all crates to workspace root

Having all the workspace crates under the crates/ directory is
unnecessary. Rust documentation itself recommends all crates to be in
the root directory:

https://doc.rust-lang.org/book/ch14-03-cargo-workspaces.html#creating-the-second-package-in-the-workspace

I paste the text content here, in case the online page ever changes or
becomes unavailable:

    ## Creating the Second Package in the Workspace

    Next, let’s create another member package in the workspace and call it add_one. Change the top-level Cargo.toml to specify the add_one path in the members list:

    Filename: Cargo.toml

    [workspace]

    members = [
        "adder",
        "add_one",
    ]

    Then generate a new library crate named add_one:

    $ cargo new add_one --lib
         Created library `add_one` package

    Your add directory should now have these directories and files:

    ├── Cargo.lock
    ├── Cargo.toml
    ├── add_one
    │   ├── Cargo.toml
    │   └── src
    │       └── lib.rs
    ├── adder
    │   ├── Cargo.toml
    │   └── src
    │       └── main.rs
    └── target

Signed-off-by: Manos Pitsidianakis <[email protected]>

Author: epilys

Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
 members = [
-    "crates/vm-superio",
-    "crates/vm-superio-ser",
+    "vm-superio",
+    "vm-superio-ser",
 ]

README.md

@@ -38,7 +38,7 @@ covered in this crate, the VMM needs to do the following operations:
 - event handling (optional)
 
 The following UART registers are emulated via the
-[`Serial` structure](crates/vm-superio/src/serial.rs): DLL, IER, DLH, IIR, LCR,
+[`Serial` structure](./vm-superio/src/serial.rs): DLL, IER, DLH, IIR, LCR,
 LSR, MCR, MSR and SR (a brief, but nice presentation about these,
 [here](https://www.lammertbies.nl/comm/info/serial-uart#regs)).
 The Fifo Control Register (FCR) is not emulated; there is no support yet for