Make use of `cargo metadata`

[qryxip]

1. To free from CWD.

   Unlike other popular Cargo commands, cargo-atcoder currently assumes that CWD equals $CARGO_MANIFEST_DIR. We will be able to run cargo-atcoder everywhere under the workspace directory.

2. To support --manifest-path and -p|--package.

   Building dependencies takes long time in general. Even proconio takes about 30 seconds with the derive feature.

   Warming up release build for `abc152`...
      Compiling proc-macro2 v0.4.30
      Compiling unicode-xid v0.1.0
      Compiling syn v0.15.44
      Compiling lazy_static v1.4.0
      Compiling quote v0.6.13
      Compiling proconio-derive v0.1.6
      Compiling proconio v0.3.6
      Compiling abc152 v0.1.0 (/home/ryo/src/local/abc152)
   warning: unused variable: `n`
    --> src/bin/b.rs:5:9
     |
   5 |         n: usize,
     |         ^ help: consider prefixing with an underscore: `_n`
     |
     = note: `#[warn(unused_variables)]` on by default
   
       Finished release [optimized] target(s) in 41.81s

   I'd like to propose that we create a large workspace and add the packages to the workspace members. In this way, we can keep using one build cache with the same dependency graph.

   (edit) Then we would have to put profile.release on the root manifest, and to rename bins uniquely.

   .
   ├── abc157
   │   ├── Cargo.toml
   │   └── src
   ├── abc158
   │   ├── Cargo.toml
   │   └── src
   ├── abc159
   │   ├── Cargo.toml
   │   └── src
   ├── Cargo.lock
   ├── Cargo.toml
   └── target
       ├── debug
       └── release

   # <workspace-root>/Cargo.toml
   
   [workspace]
   members = ["abc157", "abc158", "abc159"]
   exclude = ["abc154", "abc155", "abc156"]
   
   [profile.release]
   lto = true
   panic = 'abort'

   # <workspace-root>/abc159/Cargo.toml
   
   [package]
   name = "abc159"
   version = "0.1.0"
   authors = ["Ryo Yamashita <qryxip@gmail.com>"]
   edition = "2018"
   
   [[bin]]
   name = "abc159-a"
   path = "./src/bin/a.rs"
   
   [[bin]]
   name = "abc159-b"
   path = "./src/bin/b.rs"
   
   [[bin]]
   name = "abc159-c"
   path = "./src/bin/c.rs"
   
   [[bin]]
   name = "abc159-d"
   path = "./src/bin/d.rs"
   
   [[bin]]
   name = "abc159-e"
   path = "./src/bin/e.rs"
   
   [[bin]]
   name = "abc159-f"
   path = "./src/bin/f.rs"
   
   # Not here
   #[profile.release]
   #lto = true
   #panic = 'abort'
   
   [dependencies]
   proconio = { version = "0.3.6", features = ["derive"] }

   Currently, cargo-atcoder does not work with such a workspace. With cargo metadata, we can use cargo-atcoder on large workspaces.

[qryxip]

--no-deps for cargo metadata was not good. I'll rewrite.

[qryxip]

I will resolve the conflict.

[tanakh]

It seems to be good feature. Thank you for nice patch! Warming up time was also annoying for me.