Extend the types section of the documentation with operation semantics

[axic]

Would be important to explain unary and binary operators on integer and fixed point types.

(Raised in #3389).

[ChrisChinchilla]

@axic and @chriseth I just started looking at this, but noticed that
#3389 has a docs contribution already, so shall I just extend and polish the changes there? And work in that branch or fork a new branch from it? or just start a new branch with their commits and my polish?

[randomnetcat]

#3389's doc contributions are specifically concerning fixed point operations and semantics. I would not recommend basing anything for this task off of that.

[chriseth]

@axic is there something else to do here?

[axic]

We can open a new issue for tracking fixed point types only or request it to be filled within the fixed point PR.