build system: Fix build system

'clean' target is cleaning checks now.
lcc, lip: Improve string
gc: Clean up
Update README.md
lip: Fix memory leak in string
dts: Clean up
toolbox: Improve string
use iconv
toolbox: Add exit callback to public interface
toolbox: Improve doc comments of refcounter
toolbox: Fix hash map
toolbox: Improve doc comments of atom and update for 032fa9bfc99e28b625d5ad648c8206519ac4c6a2
toolbox: Update test suite for 032fa9bfc99e28b625d5ad648c8206519ac4c6a2
build system: Fix linking of libiconv in Linux environments
toolbox: Fix hash map
dts: Improve dts
mkx: Improve mkx