v0.4.0-preview

• Most types associated with compilation, including the Compile class itself, have been moved to the WebAssembly.Runtime namespace.
• Importing was changed from compile time (using raw MethodInfo) to instantiation time (using delegates).
• The ModuleName and FieldName properties of RuntimeImport have been removed in favor of a more JavaScript-like dictionary-of-dictionaries-of-imports at instantiation time.