Implement check for unaligned small sizes
Implement more aggressive early preload
Implement early preload catch up for line_size of 32
Add custom write alignment for RPi and fix preload offset calculation

The Raspberry Pi benefits from custom write alignment depending on the
alignment of the source. Attempt to optimize the decision to align
writes to 32 bytes or not.

The preload offset calculation was incorrect if line_size was equal
to write_align in the new "simpler" memcpy variants.