* Update free-programming-books-es.md

Add Piensa en Perl 6 (Spanish translation of Think Perl 6)

* Update free-programming-books.md

Add another Perl 6 book. Nowadays Perl 6 is also known as Raku (https://marketing.perl6.org/id/1541379592/pdf_digital) and the name Rakudo refers to the only major Perl 6 compiler at the moment. Also update status of 'Using Perl 6'.

* Update free-programming-books.md

Alphabetize list

* add space to satisfy linter

* Update free-programming-books-es.md