[de] Use "Du", "Deinen",... instead of "du", "deinen"

- See also http://www.duden.de/sprachwissen/sprachratgeber/gross-oder-kleinschreibung-von--em-du-du--em--und--em-ihr-ihr--em--1
   Use capitalized letters because in first parts of the book they are also used.
[de] Fix typos
[de] Improve german translation of chapter 7.1
[de] Use markdown extension for README file
[de] Use markdown syntax in german README file
Merge pull request #401 from fernsehkind/master

[de] Improve german translation of chapter 7.1