namespaces are wrong

[JeffGarland]

Have a look at beman.optional here:

https://godbolt.org/z/Gc6Y9j6zf

Notice:

#include <beman/optional/optional.hpp>
....
beman::optional::optional<int> empty_opt{};

The include paths and namespaces match. Now look at inplace_vector

https://godbolt.org/z/6f7Ea8P4q

#include <beman/inplace_vector/inplace_vector.hpp>
...
using namespace beman::inplace_vector;
//gives the error:
<source>:6:24: error: 'inplace_vector' is not a namespace-name
    6 | using namespace beman::inplace_vector;

That's because inplace_vector is only in the beman namespace https://godbolt.org/z/bd3ob1bf5

The standard sez:

[CPP.NAMESPACE] RECOMMENDATION: Headers in include/beman/<short_name>/ should export entities in the beman::<short_name> namespace.

It's only a recommendation, but we should follow it in my view for consistency.

Similarly if you look at details you optional you'll see this for details. https://github.com/bemanproject/optional/blob/069cd74ff18e1f3c82d054b2f7b50dc22a926509/include/beman/optional/detail/iterator.hpp#L12

Notice the namespace is beman::optional::detail. For inplace vector we have beman::detail

inplace_vector/include/beman/inplace_vector/inplace_vector.hpp

Line 33 in b8aabf6

namespace beman::details::inplace_vector {

which should be beman::inplace_vector::detail - even though the standard is silent on the matter (it probably shouldn't be).

This really should be an easy mechanical change.

[wusatosi]

Hum I originally wrote this as beman::inplace_vector to aid ergonomics, but yeah if it's in the standard I can switch it over.

[wusatosi]

Will work on this once #90 is merged.