feat(packages): URLs are allowed many more breakpoints

[Omikhleia]

Here is my proposal for #1229 - Compared to the ticket, I have ended up adding a bit more flexibility. Sounds good to me in all my tests so far (but I can't have a test submitted, as the url package needs the pdf package which needs the libtexpdf backend, not the debug backend - If I am not mistaken).

Besides a brute force test (see below), looks decent too in my "test" article:

(I would have preferred the _ tto have a break after it, not before, but toying with the penalty settings, it was not much better with a very dense line, so I think they are quite OK finally... But of course the default penalties are at best a wild guess)

The brute force test, if one wants to play with it - 12 pages of URLs 😸 - the decent scenario being of course the last.

\begin[papersize=6in x 9in]{document}
\script[src=packages/url]

\language[main=en]

1. Check the undocumented href is not broken

\href{https://my.site.org/proposition;2021/sile/test_url?name=Jack&age=50#hash-my-anchor}

2. Test url without language (default)

\script{
    local url = "https://my.site.org/proposition;2021/sile/test_url?name=John%20Doe&age=50#hash-my-anchor"
    for i = 7, 74 do
      SILE.typesetter:leaveHmode()
      for j = 1, i do
         SILE.typesetter:typeset("x")
      end 
      SILE.typesetter:typeset(" ")
      SILE.call("url", {}, { url }) 
    end
}

3a. test url with a language (English)

\script{
    local url = "https://my.site.org/proposition;2021/sile/test_url?name=John%20Doe&age=50#hash-my-anchor"
    for i = 7, 74 do
      SILE.typesetter:leaveHmode()
      for j = 1, i do
         SILE.typesetter:typeset("x")
      end 
      SILE.typesetter:typeset(" ")
      SILE.call("url", { language = "en" }, { url }) 
    end
}

\language[main=fr]

3b. test url with French: punctuation spacing rules should be disabled; except in this line!

\script{
    local url = "https://my.site.org/proposition;2021/sile/test_url?name=John%20Doe&age=50#hash-my-anchor"
    for i = 7, 74 do
      SILE.typesetter:leaveHmode()
      for j = 1, i do
         SILE.typesetter:typeset("x")
      end 
      SILE.typesetter:typeset(" ")
      SILE.call("url", { language = "fr" }, { url }) 
    end
}

\language[main=en]

4. test url with some flexible text content

\script{
    local url = "https://my.site.org/proposition;2021/sile/test_url?name=John%20Doe&age=50#hash-my-anchor"
    for i = 4, 44 do
      SILE.typesetter:leaveHmode()
      for j = 1, i do
         SILE.typesetter:typeset("x ")
      end 
      SILE.typesetter:typeset(" ")
      SILE.call("url", {}, { url }) 
    end
}

\end{document}

[alerque]

The substance of what this does looks great, thanks for the contribution. Lets just shuffle the documentation around a little bit.