Add aliases for subcommand

[Jujumba]

This PR adds several "cargo-like" aliases for common subcommands, presumably:

• b for build
• r for run
• c for check
• ls for list
• cov for coverage

The help message after the added changes:

A `cargo` subcommand for fuzzing with `libFuzzer`! Easy to use!

Usage: cargo-fuzz <COMMAND>

Commands:
  init      Initialize the fuzz directory
  add       Add a new fuzz target
  build     Build fuzz targets [aliases: b]
  check     Type-check the fuzz targets [aliases: c]
  fmt       Print the `std::fmt::Debug` output for an input
  list      List all the existing fuzz targets [aliases: ls]
  run       Run a fuzz target [aliases: r]
  cmin      Minify a corpus
  tmin      Minify a test case
  coverage  Run program on the generated corpus and generate coverage information [aliases: cov]
  help      Print this message or the help of the given subcommand(s)

Options:
  -h, --help     Print help information
  -V, --version  Print version information

So it means that one, for example, can write

cargo fuzz b <target>

instead of

cargo fuzz build <target>

[fitzgen]

Seems reasonable! Thanks!