SanderMertens#179 fix issue with redefining namespaced components in C++

SanderMertens#124 update amalgamated source

SanderMertens#179 fix issues with registering components in multiple …

…worlds with C++

SanderMertens#124 add C++ entity documentation

SanderMertens#124 fix cmake build, add example

SanderMertens#124 add ecs_set_min_count to ecs_vector_t, extend migra…

…tion guide

SanderMertens#124 add target_include_directories to cmake file

SanderMertens#124 add target_include_directories to cmake file

SanderMertens#124 fix C examples

SanderMertens#124 don't prefix entity constants for builtin tags