Refactored int16.c into multiple files

- Follows unix philosophy this way
Added the sequential read operations to the header
Refactored int24.c
refactored int32
refactored int40.c
refactored int48.c
refactored int56.c
refactored int40.c
Fixed src/cmd/freadline_test.c to be compilable
Replaced iris with libcortex in the Makefile