Choose which optional optimizations you want Sigil to perform.

Add OptimizationOptions enum with None, EnableBranchPatching and All flags.

Add OptimizationOptions arguments to the CreateMethod, CreateConstructor and CreateDelegate methods (and overloads) on Emit<DelegateType>. and pass them through to Seal to determine whether to apply branch patches.

Review the flags stuff (I'm pretty sure I got it right, but don't know if it's idiomatic flags usage).