Python interpreter and libraries/headers detection.

- The user can now pass its own interpreter.
- Development libraries and headers can be requested.
- Travis-CI switched to new container-based workers.

test/python_interpreter/src/CMakeLists.txt

@@ -0,0 +1 @@
+add_executable(example example.cpp)

test/python_interpreter/src/example.cpp

@@ -0,0 +1,7 @@
+#include <iostream>
+
+int main()
+{
+    std::cout << "PASSED";
+    return 0;
+}