Add InChI library mutex
Add InChI library mutex

This adds a single mutex to the InchiLineFormat code
which protects the non-reentrant InChI library functions.
This allows for the InchiLineFormat::read() and write()
methods to be safely called from multiple threads.

kylelutz/chemkit,kylelutz/chemkit,kylelutz/chemkit,kylelutz/chemkit