NanoTimer: split header and body

    modified:   time/nanotimer.cpp
    new file:   time/nanotimer.h
sigfpe: exception handler to prevent SIGFPE

    modified:   Makefile
    new file:   signal/sigfpe.c
    new file:   signal/sigfpe.h
Split implementation parts and test parts

    modified:   Makefile
    new file:   misc/dosgeterrormessage-test.c
    modified:   misc/dosgeterrormessage.c
    new file:   signal/sigfpe-test.c
    modified:   signal/sigfpe.c
    new file:   time/nanotimer-test.cpp
    modified:   time/nanotimer.cpp