Move ExecutionProxy to the Fixie.Execution namespace.
Because every occurrence of ExecutionEnvironment is used only to interact with ExecutionProxy methods, add convenience pass-thru methods on ExecutionEnvironment for each of the ExecutionProxy methods, simplifying all usages of ExecutionEnvironment and better revealing the intent of those usages.
ExecutionEnvironment.Create<T> is private now that it is only called by other methods on this class.
Phase out redundant first argument assemblyFullPath from ExecutionEnvironment methods, since this same string is already passed to the constructor.
ExecutionEnvironment accepts relative paths to assemblies, calling Path.GetFullPath against it immediately, so that callers to the constructor don't have to call GetFullPath themselves.
Merge pull request #68 from plioi/SimplifyAppDomainInteractions

Simplify AppDomain Interactions