Add domain specific examples

[rherrmannr]

Add example category for the domains and add examples. E.g.:

• CDomain: using a std header (stdio with println) and a simple custom header with a variable, function, struct and enum
• CppDomain: same
• JavaDomain: same

In this way, we can show what the feature does and lead some attention to it. Currently, you must know what the CDomain is and search for examples, which are using it. Thus, I believe, a lot of people do not see the language-specific domain as a feature.