This commit mostly fleshes out the cargo-binrw interface

[dmgolembiowski]

Need some assistance on some trivial things, like getting either Copy or AsRef to make the last bit work.

[dmgolembiowski]

Also I saw a trick used on miniserve's CLI where we can forego using the call to parse arguments and enable cargo binrw to simply do the default implementation on Args through a direct dispatch (after checking the length on sysargv).