Local variable cleanup

First batch of formatting fixes, submitting these before things get massively out of sync again.

I've tried to apply the following rules throughout the code:

 * Local variables should be declared within the scope in which they are used.
 * Read-only variables should be declared `const`.
 * Local variables used in only a limit range of the scope should get their own scope.

I've also tried being a bit more explicit in variable and function naming.

See merge request !113

Conflicts:
	src/engine.c

size_t

As per #70, we will run into problems with more than 2bn particles per node as all the particle counters and loop variables are currently `int`.

As a first step, switch the stored particle counts to `size_t`.

The next series of commits will be to change all the *loops* over the particles. I'm breaking this into two pieces since these changes are highly disruptive, especially since I'm submitting them along with !113.

See merge request !114

Conflicts:
	examples/main.c

Conflicts:
        src/engine.c

make all particle counters size_t instead of int. this will break a lot of stuff, the following commits will be file-by-file fixes.

Update MPI plotting script with multi step tasks

Updates the task lists.

See merge request !111

Make sure the HDF5 dataset chunks are smaller than the dataset itself.

That solves issue #116. Thanks !

No need to do anything for the parallel-HDF5 version as there is no chunking there.

See merge request !110

Code timing and verbosity

To help with the scaling tests, I have introduced two levels of verbosity.

- './swift -v 1' makes the MPI rank 1 write timing information to stdout.
- './swift -v 2' makes all MPI ranks write timing information to stdout.
- './swift' suppresses all timing information to stdout.

The 'error()' and 'message()' macros now also print the date and time.



See merge request !107

Lose a figure to keep output shorter, the field will expand as necessary

Conflicts:
	src/debug.c
	src/engine.c

Autotools update

Adds `--disable-vec` option to add the following flags:

  - GCC: ` -fno-tree-vectorize`
  - ICC: `-no-vec -no-simd`
  - CLANG: `-fno-vectorize -fno-slp-vectorize"`

There is no `--enable-vec`, that is a noop.


See merge request !108