This reduces the redundant implementations of checksum calculation to
one generic implementation, makes the checksum interface conform over
all protocols, and brings performance optimizations. For instance,
the checksum is now calculated directly in big endian which saves us
most of the previously done byte-re-ordering.
Issue #2775
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082