Operator and Assignment Symbol Support in Auto-Complete

[rosenbrockc]

When an interface defines an operator or assignment operation for a custom types, we would like isense support for using those symbols. For example custom_type = should suggest the XML documentation for the special assignment interface based on the type of the symbol to the left of "=". Since the assignment symbol can be anything (it is defined in the interface), we should support any of the custom symbols.

In a similar vein, if operators are defined with the .operator. symbol syntax, it would be nice if we got documentation support for custom_type .operator. where the operator is explained.

For both of these support implementations, we would just need to add some logic to the in_function_call() and adjust the user contextualizer to search for more than just "=" when looking for assignments and to identify custom operators.