Refactor ExcelFunctionRegistration

Refactor ExcelFunctionRegistration wrapper to keep track of all
CustomAttributes.
Add Optional / Nullable Parameter Conversions

Add an Initial implementation of parameter conversions, including
Optional and Nullable types, and type conversions for parameters and
return types.
Extra check in parameter conversion

Add extra assertion to check expectations when applying parameter conversion.
Fix typo

Fix typo made when editing online...
Separate ParameterConversionConfiguration
Add type conversions to nullable and optional
Add F# optional parameters and VB example
First implementation of MethodExecutionHandlers

Add support for method function execution wrappers allowing OnEntry,
OnSuccess, OnException and OnExit interception.
Rename MethodExecution to FunctionExecution
Fix FunctionExecutionHandler and add examples
Update Nuget  package references
Merge as MapArrayFunctionRegistration
Fix up Test project
Initial commit for VBA compatibility library

Range support does not work yet, due to type unification issues with
embedded COM interop types.
Removing hard-coded references to c:\work in build events (might need to fix Excel-DNA nuget install script?)