Move to std::make_unique
Move <c14/cstdfloat.h> to base since it's not being standardized for c++14
Remove <c14/type_traits.h>

All have been moved into <type_traits>
integer_sequence and index_sequence have been standardized.
Move <c14/apply.h> to <base/apply.h>

Also add a link to the relevant standardization progress.
c14/identity.h -> base/identity.h
Remove <c14/utility.h>

We don't use the make_*_range defined in it. Those also haven't been standardized.
Remove now-empty c14 directory