Generics support

[dalance]

This is a syntax idea for generics support.
Generics is not the same as "parameter override", it provide more flexibility than SystemVerilog.
This is because the generics code will be expanded by transpiler.

I think this resolves #39, #58 and #178 in a unified way.

In this idea, ::<> is used for generics because <> is used as packed array currently.
::<> comes from "turbofish" which is used in Rust's generics function call.

• module

module A::<T> #(
    parameter a: u32 = 1,
) (
    a: input logic,
) {
    inst u: T ();
}

module B {
    inst u: A::<ModuleC> ();
}

• struct

struct A::<T> {
    a: T,
}

var a: A::<logic<10>><10>;

• function

function FuncA::<N> (
    a: input logic<N>
) -> logic<N> {
    return a;
}

assign x = FuncA::<10>(a);

• package

package PackageA::<N> {
    localparam A: u32 = N;
}

import PackageA::<10>;