Added AssemblyReferences.cs
Changed passing references to ScriptExecutor and ScriptEngine from string to using AssemblyReferences
Fixed tests to use the new AssemblyReferences
Updated ScriptExecutor and its interface method names
Added: ScriptExecutorTests for AddReferences/RemoveReferences
Merge branch 'dev' of https://github.com/scriptcs/scriptcs into assembly
fixed failing build
Merge pull request #477 from filipw/assembly

Allow adding references to executor/engine via Assembly instance

Fixes #471.