Adds the spanish translation for the next sections:

- Quality Matters
- Don't do hard things, do easy things.
- Don't Write Code
- Stop Writing Classes
- Refactoring > Rewriting
- Rewriting > Patching
- Refining existing features > Adding new features.
- Write unit tests.
Corrects the translation of the section header "Don't Write Code"
Merge pull request #6 from adrrian17/master

Spanish translation for various sections