Overview of changes:

 *  Revamped event data model a bit

    Removed lots of repetition and useless cruft, simplified events.

 *  Added support for multi-line log messages

    Every argument to logging functions will now constitute one line of
    the final message.

    Thx @ester and @magda.

 *  jat__sfinish() will now return informative exit status

    Roughly following TFKit convention

    Case ids dynamically extend test ids from within the test, adding
    further granularity, feature linkage and promise/delivery control.

 *  Added support for t., o., and r. prefixes for assert data

    Allowed these prefixes in data key name to set convention where
    relevancy to test, oracle or and result is made more clear.

 *  Added support for saving exit status into file

    Useful in xcase when we need for the result to stay from one handler
    than other.  In that case local var cannot suffice but since context
    is already driven by working directory, using file is safe---so it's
    than a global variable.

 *  Made reloading more robust

    Now jat__sinit() Won't reload session unless test id and version match

 *  Added support for case ids

 *  Fixed error when submitting without altname

 *  Added test id and version to stderr and log

 *  Codebase cleanups and maintenance

On session init, both new and reload.

Since exit status of code-executing assert functions cannot be
guarranteed to match exit status of the code being executed, there is
now a way to get the latter in more reliable way.  This should be also
useful in cases when there are further asserts on value of the status.