devdocs notes on memory layout and runtime initialisation

Some notes I made while learning about runtime internals.
Maybe useful for other new developers.
But maybe misleading because eggnog :)

> are just implementation detail of a compiler optimisation

much of what you are attempting to document here is an implementation detail of a compiler optimization (or current lack thereof), except that they are compatible with C as documented in http://docs.julialang.org/en/latest/manual/calling-c-and-fortran-code/#type-correspondences