Revert "rename exercises (A,B, ...)"

This reverts commit f1bef415ade96788f2965321af72de3e7bb4d98a.
Solution "exercise 1.3"

This reverts commit 1ad3f52058bd229a048f4e218ae62feb86404528.
Solution "exercise 1.2"

This reverts commit 9e634ca0a6fbecf3e8e08f77a864cfa1ad19489c.
Solution "excercise 1"

This reverts commit f5617187bbee8a41dd77201055b96c3e2c2388a0.