Merge pull request #17 from steenpass/andreas

update to the first draft which was discussed with others
apply some minor changes

Most of these changes were suggested by GM.
remove algorithm for the Milnor number
add a remark on the highest corner
distinguish between theoretic and algorithmic classification
remove the section on blowing-up

use dehomogenization instead for D_4
apply some corrections and suggestions by Magdaleen and Gerhard
Merge pull request #18 from steenpass/andreas

apply corrections
final changes before submission
Merge pull request #19 from steenpass/andreas

final changes before submission