doc: fix cargo doc builds when non-default features selected

[phlip9]

While upgrading to v0.12.0 our cargo doc builds broke:

$ cargo doc --no-default-features --features=async,tokio

# ...

error: unresolved link to `minreq`
  --> /Users/phlip9/dev/esplora-client/src/lib.rs:54:42
   |
54 | //! * `blocking-https-bundled` enables [`minreq`], the blocking client with proxy and TLS (SSL)
   |                                          ^^^^^^ no item named `minreq` in scope
   |
   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`

error: public documentation for `max_retries` links to private item `RETRYABLE_ERROR_CODES`
   --> /Users/phlip9/dev/esplora-client/src/lib.rs:171:21
    |
171 |     /// is one of [`RETRYABLE_ERROR_CODES`].
    |                     ^^^^^^^^^^^^^^^^^^^^^ this item is private

# ... etc

To keep the nice doc links to minreq and reqwest, I just pointed them to https://docs.rs/minreq and https://docs.rs/reqwest respectively. It won't resolve to the exact version, but it's better than nothing IMO.

[phlip9]

Looks like MSRV CI isn't pinning lock_api to the right version?

[coveralls]

Pull Request Test Coverage Report for Build 15917138414

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 87.594%

---

Totals
Change from base Build 15916798408:	0.0%
Covered Lines:	1052
Relevant Lines:	1201

---

💛 - Coveralls

[ValuedMammal]

I'm updating the pinned deps in #130 if you want to try to build this PR on top of that.

[phlip9]

rebased on #130

[ValuedMammal]

ACK 03de52e

[notmandatory]

Thanks for fixing the docs here. I have a couple suggestions to keep the original intent when the docs are built for docs.rs.

I didn't mean to approve it here, just meant to add my comments.

[notmandatory]

You'll also need to rebase on master now that #130 is merged. Thanks!

[phlip9]

Hmm, the nightly rustfmt wants to remove this newline (though my local toolchain doesn't yet):

 //! * `async-https-rustls-manual-roots` enables [`reqwest`], the async client with support for
 //!   proxying and TLS (SSL) using the `rustls` TLS backend without using its the default root
 //!   certificates.
-//!
 #![cfg_attr(not(feature = "minreq"), doc = "[`minreq`]: https://docs.rs/minreq")]
 #![cfg_attr(not(feature = "reqwest"), doc = "[`reqwest`]: https://docs.rs/reqwest")]
 #![allow(clippy::result_large_err)]

But then cargo doc fails without the newline : /

$ cargo doc --no-default-features --features=async,tokio
 Documenting esplora-client v0.12.0 (/Users/phlip9/dev/esplora-client)
warning: unresolved link to `minreq`
  --> src/lib.rs:1:1
   |
1  | / //! An extensible blocking/async Esplora client
2  | | //!
3  | | //! This library provides an extensible blocking and
4  | | //! async Esplora client to query Esplora's backend.
...  |
65 | | //!   certificates.
66 | | #![cfg_attr(not(feature = "minreq"), doc = "[`minreq`]: https://docs.rs/minreq\n")]
   | |_________________________________________________________________________________^
   |
   = note: the link appears in this line:

           client using [`minreq`] and an async client using [`reqwest`].
                         ^^^^^^^^
   = note: no item named `minreq` in scope
   = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
   = note: `#[warn(rustdoc::broken_intra_doc_links)]` on by default

[phlip9]

Nice, got it to work with this dummy link lol

```diff
 //! * `async-https-rustls-manual-roots` enables [`reqwest`], the async client with support for
 //!   proxying and TLS (SSL) using the `rustls` TLS backend without using its the default root
 //!   certificates.
 //!
+//! [`dont remove this line or cargo doc will break`]: https://example.com
 #![cfg_attr(not(feature = "minreq"), doc = "[`minreq`]: https://docs.rs/minreq")]
 #![cfg_attr(not(feature = "reqwest"), doc = "[`reqwest`]: https://docs.rs/reqwest")]
 #![allow(clippy::result_large_err)]

[notmandatory]

ACK 6eece87

Thanks for the quick turnaround and figuring out that dummy link fix.