static compile part 3 (modules)

This prepares the serializer to be able to handle incremental loading (aka module caching). Currently there is no interface to it exposed to the user (other than the raw interface I demonstrate below for testing). Static compile part 4 to add the user-friendly interface will be developed shortly, but I wanted to go ahead and get this merged first since that is a separate task. Part 4 is expected to be easy technically but has more UI questions to answer.

```julia
julia> @time begin
           FP = ccall(:jl_restore_new_module, Any, (Ptr{Uint8},), "FixedPointNumbers_cache.jlc")
           C = ccall(:jl_restore_new_module, Any, (Ptr{Uint8},), "Color_cache.jlc")
           C2 = ccall(:jl_restore_new_module, Any, (Ptr{Uint8},), "Cairo_cache.jlc")
           G = ccall(:jl_restore_new_module, Any, (Ptr{Uint8},), "Gtk_cache.jlc")
           Gtk.GLib.__init__()
           Gtk.__init__()
       end
elapsed time: 0.691674234 seconds (14420556 bytes allocated)

julia> evalfile(Pkg.dir("FixedPointNumbers/test/runtests.jl"))

julia> evalfile(Pkg.dir("Color/test/runtests.jl"))

julia> evalfile(Pkg.dir("Cairo/test/test_speed.jl"))
<output clipped>

julia> evalfile(Pkg.dir("Gtk/test/tests.jl"))

julia> # All tests passed :)
```

note: this would have been fully compatible with the current serializer, except that I changed the deser_tag hash-table (with indexes from 0 to 255) into an array.
For consistency, they would typically get copied. Or we will just refuse to serialize a module with such a dependency. This serializer generally takes the approach that the safest way to ensure the environment is the same after reloading is to copy the entire environment. The trick with making this work well is going to be to ensure that does not become an surprise / issue for the end user.