script: link check improvements

[jonatack]

Don't raise on [url](url) or [url] in the markdown format check.

Instead, optionally flag [url](url) in a separate check with an appropriate message.

Finish with a few editorial touch-ups.

[jonatack]

Checked these changes by running the script locally against this diff:

diff

--- a/bip-0003.md
+++ b/bip-0003.md
@@ -68,7 +68,7 @@ software. Some may even end up changing the consensus rules that the Bitcoin eco
 
 ### What is the Purpose of the BIPs Repository?
 
-The [BIPs repository](https://github.com/bitcoin/bips/) serves as a publication medium and archive for mature proposals.
+The [[https://github.com/bitcoin/bips/|text]] serves as a publication medium and archive for mature proposals.
 Through its high visibility, it facilitates the community-wide consideration of BIPs and provides a well-established
 source to retrieve the latest version of any BIP. The repository transparently records all changes to each BIP and
 allows any community member to retain a complete copy of the archive easily.
@@ -80,6 +80,8 @@ No formal or informal decision body governs Bitcoin development or decides adopt
 
 ## BIP Format and Structure
 
+[[https://github.com/bitcoin/bips|text]] serves as a publication medium and archive for mature proposals.
+
 ### Specification
 
 Authors may choose to submit BIPs in MediaWiki or Markdown[^markdown] format.
@@ -111,9 +113,10 @@ following list and address each as appropriate.
 
 Each BIP must begin with an [RFC 822-style header preamble](https://www.w3.org/Protocols/rfc822/). The headers must
 appear in the following order. Headers marked with "\*" are optional. All other headers are required.
+[http://example.com]
 
 ##### Overview
-
+[https://bitcoin.com](https://bitcoin.com)

BIP: <BIP number, or "?" before assignment>

• Layer: <Consensus (soft fork) | Consensus (hard fork) | Peer Services | API/RPC | Applications>
  @@ -130,7 +133,7 @@ appear in the following order. Headers marked with "*" are optional. All other
• Replaces: <BIP number(s)>
• Proposed-Replacement: <BIP number(s)>

-
+[https://bitcoin.org https://bitcoin.org]
##### Header Descriptions

Before:

$ ./scripts/link-format-chk.sh
Github Markdown format writes links as [text](URL), not as [URL text] or [[URL|text]]:
- bip-0003.md:71:The [[https://github.com/bitcoin/bips/|text]] serves as a publication medium and archive for mature proposals.
- bip-0003.md:83:[[https://github.com/bitcoin/bips|text]] serves as a publication medium and archive for mature proposals.
- bip-0003.md:116:[http://example.com]
- bip-0003.md:119:[https://bitcoin.com](https://bitcoin.com)
- bip-0003.md:136:[https://bitcoin.org https://bitcoin.org]

After:

$ ./scripts/link-format-chk.sh                            
GitHub Markdown format writes links as [text](URL), not as [URL text] or [[URL|text]]:
- bip-0003.md:71:The [[https://github.com/bitcoin/bips/|text]] serves as a publication medium and archive for mature proposals.
- bip-0003.md:83:[[https://github.com/bitcoin/bips|text]] serves as a publication medium and archive for mature proposals.
- bip-0003.md:136:[https://bitcoin.org https://bitcoin.org]
Markdown links where the text matches the URL are redundant. Use <URL> instead:
- bip-0003.md:119:[https://bitcoin.com](https://bitcoin.com)

[murchandamus]

ACK