doc: the Intel C++ compiler does not work

It seems that version 14.0 supports all required C++11 features. Still,
compilation fails with errors, which need further inspection.
add benchmarking results for 1.0-alpha1

The results were obtained on Hydra at the Rechenzentrum Garching of the
Max Planck Society.
doc: clean-up FAQ
benchmarks: fix output interval to H5MD files

Subsequent calls to sampler:run() trigger the signals "prepare" and "finalize"
repeatedly. If the phase_space writer is connected without explicit sampling
interval, this causes the following exception due to repeated writing at the
same simulation step:

[19-05-2014 11:39:22.152845] [ERROR] Writing to H5MD file failed at step 10000
H5MD enforces a strictly increasing order.
stack traceback:
        [C]: in function 'run'
        ...almd/examples/benchmarks/lennard_jones/run_benchmark.lua:94: in function 'lennard_jones'
        ...almd/examples/benchmarks/lennard_jones/run_benchmark.lua:141: in main chunk
[19-05-2014 11:39:22.152994] [WARNING] HALMD aborted
update submodule libs/h5xx

* libs/h5xx c056018...8354c9d (1):
  > test: explicitly link against "dl"
integrators (gpu): reduce memory access, fix bug with g_image

For most particles, the image vector is likely to remain unchanged in
one invocation of the kernel. Thus, reading and writing the image vector
in any case wastes bandwidth.

The change revealed a severe bug in the Andersen and Nosé-Hoover
thermostats: the image vector was never written back. The bug is
probably only relevant if tagged particle displacements over long times
are considered, e.g., in the computation of the MSD. In this case, the
unmodified dynamics (i.e., without thermostat) should be used.

Nevertheless, it is embarrassing that the bug was not detected by any of
the unit tests.

Results from the Lennard-Jones benchmark (before/after the patch) for
the first step of the velocity-Verlet integrator (64,000 particles):

    Tesla T10:  255 µs → 215 µs
    Tesla K20:   95 µs →  85 µs