Example for c API usage

[profhsgill]

I have read the tester.c file and it will work within the repo environment. If somebody is going to use the library in their own code, additional information is perhaps needed in the code they will write.

Is it possible that a simple c code can be provided as an example.

Say solving a simple system:

x − y = −1
y = x*x + 1
Solutions are (x=1, y=2) and (x=0, y=1)