ols: Allow disabling all channels.

This fixed bug 316.
output/ascii/bits/hex: Remove stray g_free().
WIP
fx2lafw: Don't send more samples than requested.

It's the new law.
Remove orphaned prototype for sr_filter_channels from proto.h.
SWIG: Remove obsolete lowlevel wrapper methods for sr_output_format.
SWIG: Rename libsigrok.i to lowlevel.i.
Python: Add support for session source callbacks in lowlevel wrapper.
Give type names to all enumerations.
configure.ac: Separate library flags from other CFLAGS.
Add C++ bindings.
Python: Reimplement high level bindings on top of C++ ones.
Add Java bindings.