Revert some changes since the latest published (#167)

Rolls back some changes which are not trivially safe out of caution so
that the first stable version published will match exactly with the last
published pre-release. These changes will be rolled forward in a feature
release - they are expected to be non-breaking and internal code is
already using this version.

This reverts commits
- 2071cfd84b3ede7277c57d122ef8c74cf0f3c6f0
- 71eeaee1cb8235a47e47bcad9134f744bb1c594a
- 63f1110a657fb5e2dc378db8895fef7b0a13ab30

This does not revert one code change which makes the migration easier
for users using the `same` matcher against nullable types.
- 5d52720b8cdb8ddcc4256950618650e7eabc4176