Faster project conversion, better feedback

• Known issue: Breaks VS2017 support - please use 8.0.1
• Improve performance and feedback for large projects containing large files

API

• IEnumerable<Task> becomes IAsyncEnumerable
• Upgraded target framework from netstandard 1.3 to netstandard 2.0
• Introduced cancellation token

VB -> C#

• Convert "Handles" in some previously missed cases #530
• Wrap event handlers in lambda where needed #474
• Streamline trailing else if 810de96
• Use less error-prone, more performant null/default comparisons 4de1978
• Convert "{}" to "Array.Empty()" #495
• Convert inferred anonymous member names without duplicating name #480
• Convert "!" operator to element access #479
• Fix async method default return statements #478
• Convert multi-dimensional array initializers correctly #539

C# -> VB

• Convert PrefixUnaryExpression (Not, minus, etc.) #533
• Rename more members with case conflicts (e.g. interface members) #533
• String equality conversion now calls "Equals" to match the C# logic #533
• Deduplicate imports #533
• Converts "default" keyword to "Nothing" keyword #428