Translated "es_chapter4.txt"->"capítulo4.txt"

Note: I just assumed what the links to code files (e.g. http://invpy.com/adivinaElNúmero.py) may end up looking like. They need to be reviewed. This comment applies also to other chapters.

I have also:
- suggested typo corrections in "chapter4.txt"
- added new words to "glosario.txt"
- translated "es_chapter4.figures"->"capítulo4.figuras"