More idiomatic argument parsing

[kjvalencik]

There is currently some strange argument parsing with = delimiters and a magic $npm_package_name variable. Instead we should parse as follows:

# All flags can be declared many times

# Default. Always exactly 3 arguments following `--artifact`
--artifact crate-type crate-name output-file

# Shorthand
-a crate-type crate-name output-file

# NPM special version that uses the `$npm_package_name` environment variable for crate-name
# Always exactly 2 arguments
--npm crate-type output-file

# Shorthand
-n crate-type output-file

# Lastly, modifiers can be added to the shorthand versions to apply the crate type
# b = bin
# c = cdylib
# d = dylib
# Modifiers take the place of crate-type and reduce the arguments followed by 1
# Neon would default to using
-nc output-file

We will keep the -- separator for clarity.

cargo-cp-artifact -nc index.node -- cargo build --message-format=json-render-diagnostics