Add custom return code handler for initialization call

[ReneeVandervelde]

The initialization call returns an additional code 1 if the initialzation has already completed successfully. Added a specific handler for this functionality into the common sources.

@ionspin -- I noticed when dding this code that the javascript implementation doesn't appear to be using the same return code handling as the rest for this call. I left it as-is for now, but is that an oversight or is there something else that handles that?

Fixes #67

[ionspin]

@ionspin -- I noticed when dding this code that the javascript implementation doesn't appear to be using the same return code handling as the rest for this call. I left it as-is for now, but is that an oversight or is there something else that handles that?

The JS integration was peculiar because libsodium-js already is a shallow wrapper around libsodium, so the API is not the same. Looking here, it seems the JS will throw an exception if result is not 0 when initializing

https://github.com/jedisct1/libsodium.js/blob/d3aedf1ce0ed8553ca5f2c2a8f5c0f13d369a4ba/wrapper/wrap-template.js#L11-L15

[ionspin]

Looks good, thanks @ReneeVandervelde !