Statment on thread safety missing in the documentation

[franzhollerer]

I miss some statement on thread safety in the documentation.

The commit 23313e8 removed the following text:

A libmodbus 'context' is thread safe and may be shared among as many application
threads as necessary, without any additional locking required on the part of the
caller.

and the file NEWS states for libmodbus 3.1.3 (2016-05-11):

- A libmodbus context isn't thread safe and won't be (closes #246).

But what does that mean specifically? Is the whole library not thread safe? Can I call library functions from different threads as long as I ensure that each thread operates on its own libmodbus context? Can I run a libmodbus server and libmodbus clients in different threads, or are or are there limitations to consider?

Being said, I think the documentation should have a section about thread safety.