Improve renderization of RTL (Right-to-left) languages

[dbaio]

Summary

Improve renderization of RTL (Right-to-left) languages

<screen> and <programlisting> are always ltr and align to the left
because they usually have pieces of code and commands.

This will lock <screen> and <programlisting> and RTL languages
won't change that.

Test Plan

https://dbaio.bs2cloud.com.br/doc/20200607-css-ltr/en_US.ISO8859-1/articles/ipsec-must/article.html
https://dbaio.bs2cloud.com.br/doc/20200607-css-ltr/fa_IR.UTF-8/articles/ipsec-must/article.html

https://dbaio.bs2cloud.com.br/doc/20200607-css-ltr/en_US.ISO8859-1/articles/ipsec-must/article.epub
https://dbaio.bs2cloud.com.br/doc/20200607-css-ltr/fa_IR.UTF-8/articles/ipsec-must/article.epub

https://dbaio.bs2cloud.com.br/doc/20200607-css-ltr-htdocs/
https://dbaio.bs2cloud.com.br/doc/20200607-css-ltr/en_US.ISO8859-1/books/porters-handbook/book.html
https://dbaio.bs2cloud.com.br/doc/20200607-css-ltr/en_US.ISO8859-1/books/handbook/book.html

[bcr]

I'm good with this change, thanks for working on it.
I'd wait a few more days to give other doceng members a chance to comment.