Add error messages for kramdown

[flaviut]

The kramdown filter does not do anything with the messages that kramdown outputs, which makes debugging invalid markdown more difficult.

I'm not sure about the best way to output them, just print them out once the document has been processed?

[gpakosz]

Well I just made the following test:

$ irb
irb(main):001:0> require 'kramdown'
=> true
irb(main):002:0> Kramdown::Document.new('{:foo}this is bogus').warnings
=> ["Found span IAL after text - ignoring it"]

But

irb(main):002:0> require 'kramdown'
=> true
irb(main):003:0> Kramdown::Document.new('this is a [link]
irb(main):004:1'
irb(main):005:1' [link]: foo
irb(main):006:1' [link]: bar').warnings
=> ["Duplicate link ID 'link' on line 5 - overwriting"]

After having discussed with @gettalong it happens not all warnings have line number information so it's not always possible to trace back to the offending Markdown fragment.

While discussing with @gettalong, I wondered whether the warnings array could become an array of hash so that kramdown gives does the job of tracking the line number, the offending content fragment (line excerpt etc).

Then, how would move on from the point kramdown gets more detailed warnings reporting? @ddfreyne, should the kramdown filter format a message to $stderr or is there facility in nanoc we should use to report errors/warnings (something that would understand the verbose flag).

[denisdefreyne]

There's no warning reporting system other that writing to $stderr. Errors are generally exceptions.

I could adjust the kramdown filter to print warnings, if any, but I fear that it’d cause spam on the screen that people will ignore. Seem like a good idea to do it anyway though.

[denisdefreyne]

Potential fix in #519.

[denisdefreyne]

Fixed by #519. Fix will be in 3.7.5!