Static assertions for template type properties required

[t-b]

While working on #1722 I realized that I'm relying on quite a few properties of NumberUnsignedType and NumberIntegerType.

These are:

• NumberUnsignedType is an unsigned integer
• NumberSignedType is a signed integer
• every positive NumberSignedType can be expressed as NumberUnsignedType

Do we need static_assert enforcing that?

One could put it into basic_json::assert_invariant.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[t-b]

unstale.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[t-b]

unstale.

[nlohmann]

@t-b Thanks for keeping the stale bot away. However, there was no activity since August 27. Would you have time to propose a PR?

[t-b]

@nlohmann Yes if you think this is good idea I can propose one. I just wanted to know from you before if you think this is a good idea.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.