Support default InChI (Key) generation

[BrillBay]

Background
The current Indigo-InChI support implements some magical adjustments to the options used by the generator. In fact, the code does something like this:

   iterate the all stereocenters
       if (type == MoleculeStereocenters::ATOM_AND)
            setOptions("/SRac");
        else if (type == MoleculeStereocenters::ATOM_OR)
            setOptions("/SRel");

This setOptions changes the options for all follow-up calls to the InChI with other molecules.

This has two implications:

• Depending on the order of molecules used to call the generator, the result might differ for specific molecules (if you had already called it with some stereo before or not). You can circumvent that by calling resetOptions() before each call.
• There is no chance to really control the generator:
  • No chance to force the generation of standard InChIs.
  • No chance to provide other options.
    This is a major problem for us because we are working with molecules from different systems that have already assigned standard InChI keys. There is no way to compare this with the InChI key we have generated using Indigo.

From my understanding, InChI (keys) are designed to be system-independent, and this magical adjustment of the options is exactly the opposite.

Solution
Provide a new method (or possibly a parameter to the existing one) to allow for exact control of all options to be used.

Alternatives
Add a way to set the options to be used globally.

Additional context

[BrillBay]

Robert has created a PR that adds an options parameter. If set to an empty string, indigo will always generate a std inchi without using any parameters. Or you provide the paramters you like to use.
The impl is backward compatible, omitting the parameter (or using null/none) falls back to the existing implementation (magic). Unit tests included.
Looking forward for feedback.