Incompatible with crates using newer versions of bindgen/clang-sys

[ExpHP]

There is a known issue that the current version of lammps-sys is incompatible with crates that use recent versions of bindgen or clang-sys.

This is due to problems upstream. Basically, we're waiting for a number of upstream crates to update their dependencies:

• You cannot have multiple versions of clang-sys due to it declaring the links property.
• libffi-sys uses an old bindgen that uses an old clang-sys
• mpi-sys uses libffi-sys and therefore must also use an old bindgen
• lammps-sys uses mpi-sys and therefore must also use an old bindgen

[ExpHP]

Okay, so...

libffi-sys updated their bindgen dependency, but they didn't perform a semver major bump. This has caused a bit of a mess; I opened tov/libffi-sys-rs#21 .

A version of mpi-sys with the new bindgen dependency exists on github, but is not yet released.

[ExpHP]

now just waiting on mpi-sys 0.2.0 to be released