UX: Maybe subcommands should be the 1st argument instead of options

[noncombatant]

This is an arguable style matter. But I find the 'modern' style of go and git a bit easier to use. E.g.:

age decrypt options...

age encrypt options...

Then you'd get rid of -d, --decrypt, and -r and -p would no longer implicitly mean "encrypt". It'd be explicit.

[noncombatant]

I should also add: This allows the possibility of combining age and age-keygen, by creating an age keygen subcommand. Then there'd only be 1 binary, and possibly more code sharing.

[ovalseven8]

See #22

[FiloSottile]

There is now an optional --encrypt for being explicit in scripts, but probably too late to switch to subcommands.