Fix memory leak in spiflash example.
Enhance Makefile for examples.

Add CFLAGS with '-g -Wall'.

Compile and link using headers and library in build dir to allow
building the examples without having to install the library.
Change bitbang example to drive 8 pins.

Loops over 8 pins toggling each pin on then off in turn.
Change gpio exampled to drive 4 bits.

Loops over GPIOL0 -> GPIOL3, toggling each on then off in turn.