[FIX] Removing deprecated keyword "register".

clang++-3.4 complains about it.

Also see http://stackoverflow.com/questions/10675072
[FIX] Removing more occurences of keyword "register".
[FIX] Some more forgotten register keywords.
[FIX-#235] Header guard fixes.
Merge pull request #254 from holtgrewe/feature/remove_register_keyword

[FIX] Removing deprecated keyword "register".