Adding support to inject custom converters

[iarly]

My expression has integer numbers operating with nullable decimals. In this case, an expression compatibility problem happens when I parse a simple multiplication: x * 100, where x is a nullable decimal parameter.

Then, I needed to extend the conversion behavior to enable custom number conversions that can be passed by the developer through parameters.

After this implementation, I solved my problem writing a custom IntegerConverter in my project. This custom IntegerConverter converts all numbers to decimal.

[davideicardi]

Thanks @iarly for your merge request, really appreciated.

What happen when writing an expression like this in C#?

When possible I always try to mimic the C# behaviour. So if we can use the same rules I prefer, but eventually adding some extensions should be fine...

Also maybe I prefer to have converters specified using something like interpreter.AddConverters, instead of adding more parameters to the Parse function. What do you think?

[nike61]

@iarly check my PR: #89. Maybe it will help you

[davideicardi]

I will close the PR for inactivity. Feel free to reopen if you still need this PR.