In order to allow easy debugging of some programs and runtimes, it is
often neccessary to add extra information in the timeline views. The
modification of the emulator to accomodate those temporal events is time
consuming and requires knowlegde of the emulator internals.
To improve the situation, a new set of functions are added to libovni
which allow users to define their own views. Up to 100 types of events
can be declared, where each type can have an unlimited number ov values
with an optional label attached.
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).
