refactor: Port to clap3

Ths does remove the specialization of version's description.  The way
this is done (internally through `mut_arg`) doesn't play well with
subcommands.  Clap tries to force this version of `version` into the
subcommand despite not being needed.  Clap v4 dramatically changes how
version customization works.

clap also does more error checks now to prevent programmer mistake, so
we can't have a conflict with an argument that is conditionally there,
so I swapped the condition.

Cargo.toml

@@ -77,10 +77,10 @@ default-features = false
 features = ["parsing"]
 
 [dependencies.clap]
-version = "2.34"
+version = "3.2.20"
 optional = true
 default-features = false
-features = ["suggestions", "color", "wrap_help"]
+features = ["std", "suggestions", "color", "wrap_help", "cargo"]
 
 [dev-dependencies]
 assert_cmd = "2.0.4"
@@ -93,7 +93,7 @@ tempfile = "3.3.0"
 nix = { version = "0.24.2", default-features = false, features = ["term"] }
 
 [build-dependencies]
-clap = { version = "2.34", optional = true }
+clap = { version = "3.2.20", optional = true }
 
 [profile.release]
 lto = true