move nothing, make_unique, to_unique from rx to Si
move integer_sequence to silicium/
remove rx::get because you should not use that (yet)
rename variant_observable.hpp
remove launch_process stub
unify the implementations of to_unique
move rx headers to silicium/
merge namespace rx into Si
move Windows stuff from rx into Si namespace
remove CMake find script for reactive
fix find_package_test