fix compilation on 64-bit Linux systems
extend base-type definitions for 64-bit (preliminary)
add actual 64-bit types, use for time
use dedicated 64-bit type for time variables
update description, add future extensions
add naming scheme for extended register files
increase rcp, sqr precision for ARM
fix: increase div, sqr precision for ARM NEON, rcp unchanged
fix div in ARM to use signed integers
move future extensions to rtarch