Explicitely specify C and C++ standards to use

This does not change anything, it just makes the defaults explicit.
Enable C++11 support

This uses the gnu++11 standard, which is C++11 with GNU extensions.
C++11 should be full compatible with the previously used C++98
standards, so all pre-existing sketches should continue to work.
Check for __cplusplus >= 201103L as well as __GXX_EXPERIMENTAL_CXX0X__

Gcc 4.8 defines __cplusplus as 201103L, so we can check for that now. It
still also defines __GXX_EXPERIMENTAL_CXX0X__, but this could help on
other compilers, or if gcc ever decides to stop defining the
experimental macro.
Merge pull request #3 from matthijskooijman/ide-1.5.x-c++11

Ide 1.5.x c++11