The ovni_attr_* set of functions allows users to write and read metadata
stores in the thread stream. The metadata information is available to
the emulator at the beginning of the emulation.
Traces with metadata version 1 don't use per-thread information, so we
cannot read the 'require' key. All models will be enabled for old traces
(which will cause performance problems).
The public includes are now in include/ and in internal includes in
src/include/. The ovni* tools are moved to emu/ovni*.c and liked with
the emu static library.
