Bugfix release

Unfortunately v3.0.0 introduced some severe memory leaks due to the new handling of Sass_Values. Did a lot of memory smoke tests and integration tests with the help of cpantesters.

Lowered the need for a modern gcc/clang compiler by using std=c++0x instead of std=c++11, which seems to work with clang compilers. Also fixed some minor documentation issues and other left-overs.