Rename nand.h as flash/nand/core.h, chase consumers. The public APIs
need to be sorted out with imp.h, but this allows other changes to
begin improving the separation between policy and mechanism.
Moves #include <target/target.h> and #include "driver.h" into the
internal headers or source files, removing it from <flash/nand/core.h>.
Before we can -I the top-level src/ directory alone, references to
"hello.h" must be updated. This is an internal header, so it does
not need angle brackets.
Changes from the flat namespace to heirarchical one. Instead of writing:
#include "nand.h"
the following form should be used.
#include <flash/nand.h>
The exception is from .c files in the same directory.
