Add Travis CI builds and tests

e.g. The first symbol would be blank/corrupted when running:
    printf("%s %s\n", func, func)

This was caused by a dodgy conversion from std::string
to C-string, where the result of ".c_str()" was being
saved, but the underlying std::string was modified by
the vector it was being stored in, invalidating the C-string

fix for #18: initializing comm memory

Static linking can be selected with -DSTATIC_LINKING:BOOL=ON

BCC API for attaching tracing events has been cleaned up - no more perf
readers

Store number of online CPUs, so we don't need to read /sys/devices/system/cpu/online while probes are running