tidy-up: Markdown, clang-format nits

- drop leading indent from Markdown.
- switch to Markdown section markers where missing.
- move `&&` and `||` to the end of the line (C, Perl).
- openssl: add parenthesis to an if sub-expression.
- misc clang-format nits.
- unfold Markdown links.
- SSL-PROBLEMS.md: drop stray half code-fence.

Closes #20402

.github/CONTRIBUTING.md

@@ -4,26 +4,19 @@ Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
 SPDX-License-Identifier: curl
 -->
 
-How to contribute to curl
-=========================
+# How to contribute to curl
 
-Join the community
-------------------
+## Join the community
 
 1. Click 'watch' on the GitHub repo
-
 2. Subscribe to the suitable [mailing lists](https://curl.se/mail/)
 
-Read [CONTRIBUTE](/docs/CONTRIBUTE.md)
----------------------------------------
+## Read [CONTRIBUTE](/docs/CONTRIBUTE.md)
 
-Send your suggestions using one of these methods:
--------------------------------------------------
+## Send your suggestions using one of these methods:
 
 1. in a mail to the mailing list
-
 2. as a [pull request](https://github.com/curl/curl/pulls)
-
 3. as an [issue](https://github.com/curl/curl/issues)
 
 / The curl team