Fix for bad id whitespace collapsing in references

[facelessuser]

This fixes #742 by generally collapsing all whitespace down to a single space in reference ids opposed to the previous logic of collapsing only newlines preceeded by whitespace.

[vincentbernat]

Works fine for me and it doesn't change anything on my existing set of markdown documents where I avoided to run into this case. Thanks!

[waylan]

I'm thinking we need another test. I doubt this would be a problem, but lets make sure this doesn't break things were we shouldn't get a link. For example, a blank line between the two lines:

I would like to tell you about the [code of

conduct][] we are using in this project.

That specific example shouldn't be a problem as the two halves are in different paragraphs (and therefore not in the same block of text), but it illustrates my concern: If the new regex was run against that block of text, it would strip out the blank line in addition to any other extra whitespace. And that would be an error.

I'm just not coming up with an example that might actually occur. I want to make sure we have given it some thought and, at the very least, confirm that the above example works as expected.

[facelessuser]

I imagine the stated example will work as expected. I'm happy to put it in.

I'm also having difficulty coming up with something desired that this could break. Currently, no existing tests fail, so that is a plus. This may be something, that in time, someone will have a contrived example we must account for, but currently I cannot come up with one.

[waylan]

I agree that any read-world failure would likely be from a rather contrived edge case that we are not likely to think up ahead of time. That said, I think we need to add some test to show that we at least considered it.

[facelessuser]

That said, I think we need to add some test to show that we at least considered it.

I agree. Hopefully I'll get to it later today.

[facelessuser]

Requested check is in and is passing as expected.

[waylan]

I just realized this needs a comment in the release notes. A one-liner under bug fixes should suffice.

[facelessuser]

Added.