Cargo command help

```cargo <command> help``` shows the real binary from src/bin and not the "user command".

Example:

```
$  cargo new -h
Create a new cargo package at <path>

Usage:
    cargo-new [options] <path>
    cargo-new -h | --help

Options:
    -h, --help          Print this message
    --git               Initialize a new git repository with a .gitignore
    --bin               Use a binary instead of a library template
    -v, --verbose       Use verbose output
```

This PR changes every Usage section to use the "user command".

Example:

```
$  cargo new -h
Create a new cargo package at <path>

Usage:
    cargo new [options] <path>
    cargo new -h | --help

Options:
    -h, --help          Print this message
    --git               Initialize a new git repository with a .gitignore
    --bin               Use a binary instead of a library template
    -v, --verbose       Use verbose output
```