Move macros for pointer manipulation into a separate header.
Update .gitignore with more OSX specific stuff.
Store NETPROT_VERSION in a top level variable to allow it to be easily changed.
Add netprot_header_decode to validate and decode a packed netprot struct from a void pointer of binary data.

Initial tests are also included, will complete later.
Move __attribute__ declaration for readability.
Use C instead of C++ compiler if possible.
Delete OSX specific file test_netprot_header.SYM on clean.