Fix most of clippy warnings

[tesuji]

Note: Feel free to squash this PR.

There are 3 remained warnings:

• large_enum_variant
• module_inception
• should_implement_trait

Remaining clippy warnings

warning: large size difference between variants
   --> src/errors.rs:17:1
    |
17  | / error_chain! {
18  | |     links {
19  | |         Download(download::Error, download::ErrorKind);
20  | |     }
...   |
322 | |     }
323 | | }
    | |_^
    |
    = note: #[warn(clippy::large_enum_variant)] on by default
help: consider boxing the large fields to reduce the total size of the enum
   --> src/errors.rs:17:1
    |
17  | / error_chain! {
18  | |     links {
19  | |         Download(download::Error, download::ErrorKind);
20  | |     }
...   |
322 | |     }
323 | | }
    | |_^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#large_enum_variant
    = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

warning: module has the same name as its containing module
 --> src/dist/mod.rs:9:1
  |
9 | pub mod dist;
  | ^^^^^^^^^^^^^
  |
  = note: #[warn(clippy::module_inception)] on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#module_inception

warning: module has the same name as its containing module
 --> src/utils/mod.rs:6:1
  |
6 | pub mod utils;
  | ^^^^^^^^^^^^^^
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#module_inception


warning: defining a method called `from_str` on this type; consider implementing the `std::str::FromStr` trait or choosing a less ambiguous name
   --> src/dist/dist.rs:113:5
    |
113 | /     pub fn from_str(name: &str) -> Self {
114 | |         TargetTriple(name.to_string())
115 | |     }
    | |_____^
    |
    = note: #[warn(clippy::should_implement_trait)] on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#should_implement_trait

warning: defining a method called `from_str` on this type; consider implementing the `std::str::FromStr` trait or choosing a less ambiguous name
   --> src/dist/dist.rs:213:5
    |
213 | /     pub fn from_str(name: &str) -> Option<Self> {
214 | |         if name.is_empty() {
215 | |             return Some(PartialTargetTriple {
216 | |                 arch: None,
...   |
248 | |         })
249 | |     }
    | |_____^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#should_implement_trait

warning: defining a method called `from_str` on this type; consider implementing the `std::str::FromStr` trait or choosing a less ambiguous name
   --> src/dist/dist.rs:253:5
    |
253 | /     pub fn from_str(name: &str) -> Result<Self> {
254 | |         let channels = [
255 | |             "nightly",
256 | |             "beta",
...   |
290 | |         }
291 | |     }
    | |_____^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#should_implement_trait

warning: defining a method called `from_str` on this type; consider implementing the `std::str::FromStr` trait or choosing a less ambiguous name
   --> src/dist/dist.rs:343:5
    |
343 | /     pub fn from_str(name: &str) -> Result<Self> {
344 | |         let channels = [
345 | |             "nightly",
346 | |             "beta",
...   |
374 | |             .ok_or(ErrorKind::InvalidToolchainName(name.to_string()).into())
375 | |     }
    | |_____^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#should_implement_trait
</details>

[kinnison]

Wow, this is a big PR. It will need to take quite a bit of time to be able to review it all. But thank you for doing this work.

If anyone else wants to review this, please please tell me, otherwise I'll try and set aside an hour or so soon.

[tesuji]

Rebased on master.

[bors]

☔ The latest upstream changes (presumably #1744) made this pull request unmergeable. Please resolve the merge conflicts.

[nrc]

Looks good, thanks! I had one comment, but you can ignore it. Needs a rebase

[tesuji]

Rebased on master.

[kinnison]

If you could fold the formatting updates into whichever commit they belong then I'm OK to merge this

[kinnison]

Did you mean to squash the entire branch into one commit? If so then that's fine, but if you meant to keep the different fixes independent then you might want to sort that out :D

[tesuji]

I squashed this to one commit because all those small commits only serve
one purpose: fix clippy warnings.
It's ready to merge now.