By default, clap orders command alphabetically, which can be quite
confusing when listing commands with `--help`:
```
SUBCOMMANDS:
eval Evaluate an Untyped Plutus Core program
flat Encode textual Untyped Plutus Core to flat bytes
fmt Format an Untyped Plutus Core program
help Print this message or the help of the given subcommand(s)
unflat Decode flat bytes to textual Untyped Plutus Cor
```
It is possible to instrument clap to order commands in the same way
they are declared in the source, giving us back the freedom to order
and group them in a manner that makes sense, e.g.:
```
SUBCOMMANDS:
fmt Format an Untyped Plutus Core program
eval Evaluate an Untyped Plutus Core program
flat Encode textual Untyped Plutus Core to flat bytes
unflat Decode flat bytes to textual Untyped Plutus Cor
help Print this message or the help of the given subcommand(s)
```
This follows a simple convention:
- `main.rs` contains as little as possible and delegates both
data-types definitions and command executions to sub-modules.
- modules are named after their respective commands. For
sub-commands,
- Each command module can be in one of two forms:
- Either it is a leaf command, and it then contains an `Args`
struct that defines the command arguments; and a function
`exec` when outlines the execution logic.
- Or, it is a group command with multiple sub-commands. In which
case the module defines a `Cmd` struct encapsulating all
sub-commands; and also an `exec` function which simply
dispatches the logic to sub-functions.
---
This commit also removes the `dev` command which is currently
unused. The rationale being: if it's not there, it's not there.
