use cargo workspace feature (#340)

For now, everything has been moved as it is in the "cli"
workspace. The next step is to separate the "lib" from the "cli".

cli/src/compl/compl_args.rs

@@ -0,0 +1,39 @@
+//! Module related to completion CLI.
+//!
+//! This module provides subcommands and a command matcher related to completion.
+
+use anyhow::Result;
+use clap::{self, App, Arg, ArgMatches, Shell, SubCommand};
+use log::{debug, info};
+
+type OptionShell<'a> = Option<&'a str>;
+
+/// Completion commands.
+pub enum Command<'a> {
+    /// Generate completion script for the given shell slice.
+    Generate(OptionShell<'a>),
+}
+
+/// Completion command matcher.
+pub fn matches<'a>(m: &'a ArgMatches) -> Result<Option<Command<'a>>> {
+    info!("entering completion command matcher");
+
+    if let Some(m) = m.subcommand_matches("completion") {
+        info!("completion command matched");
+        let shell = m.value_of("shell");
+        debug!("shell: {:?}", shell);
+        return Ok(Some(Command::Generate(shell)));
+    };
+
+    Ok(None)
+}
+
+/// Completion subcommands.
+pub fn subcmds<'a>() -> Vec<App<'a, 'a>> {
+    vec![SubCommand::with_name("completion")
+        .aliases(&["completions", "compl", "compe", "comp"])
+        .about("Generates the completion script for the given shell")
+        .args(&[Arg::with_name("shell")
+            .possible_values(&Shell::variants()[..])
+            .required(true)])]
+}

cli/src/compl/compl_handlers.rs

@@ -0,0 +1,21 @@
+//! Module related to completion handling.
+//!
+//! This module gathers all completion commands.  
+
+use anyhow::{anyhow, Context, Result};
+use clap::{App, Shell};
+use log::{debug, info};
+use std::{io, str::FromStr};
+
+/// Generates completion script from the given [`clap::App`] for the given shell slice.
+pub fn generate<'a>(mut app: App<'a, 'a>, shell: Option<&'a str>) -> Result<()> {
+    info!("entering generate completion handler");
+
+    let shell = Shell::from_str(shell.unwrap_or_default())
+        .map_err(|err| anyhow!(err))
+        .context("cannot parse shell")?;
+    debug!("shell: {}", shell);
+
+    app.gen_completions_to("himalaya", shell, &mut io::stdout());
+    Ok(())
+}

cli/src/compl/mod.rs

@@ -0,0 +1,9 @@
+//! Module related to shell completion.
+//!
+//! This module allows users to generate autocompletion scripts for their shells. You can see the
+//! list of available shells directly on the [clap's docs.rs website].
+//!
+//! [clap's docs.rs website]: https://docs.rs/clap/2.33.3/clap/enum.Shell.html
+
+pub mod compl_args;
+pub mod compl_handlers;