[kramdown] images attributes on new line are ignored

[zkamvar]

When processing images, a pattern like this is ignored by the parser so that the kramdown to pandoc conversion misses it:

tmp <- withr::local_tempfile()
writeLines(c("![test image](https://example.com/img.jpg)", "{.image-with-shadow width='50%'}"), tmp)
pegboard::Episode$new(tmp)$use_sandpaper()$show()
#> ---
#> ~
#> ---
#> 
#> ![](https://example.com/img.jpg){alt='test image'}
#> {.image-with-shadow width='50%'}

^{Created on 2023-04-18 with reprex v2.0.2}

[zkamvar]

Note: this still needs a bit of work because figure attributes on new lines are not allowed (afaict):

pandoc::pandoc_convert(text = "![a](link)\n{alt='b'}", to = "html")
#> <p><img src="link" alt="a" /> {alt=‘b’}</p>
pandoc::pandoc_convert(text = "![a](link){alt='b'}", to = "html")
#> <figure>
#> <img src="link" alt="b" />
#> <figcaption>a</figcaption>
#> </figure>

^{Created on 2023-04-18 with reprex v2.0.2}