[BUILD] Make the binaries only needed for the user

User can specify which binaries he needs on the commandline.

'make hex' will build examples with generating hex file
'make hex bin' will build hex and bin output
'make images' will build all images as in previous versions of buildsystem
'make all' or 'make' will build only elf files

This will have huge impact on build speed.
For the 'map' target to work correctly, this commit depends on libopencm3/libopencm3#262 of the library and #50 of the examples

This solves issue #48