testing hw_handlers with vm: only works if first MB is unmapped
that is where vector tables are setup
so need to enable high vectors
* last MB, where high vectors are, already mapped now
high vector tables work
need to add offset since handler function addresses are the ones when initially loaded
moved stacks to new kern DS location, 4K below high vector tables
implemented heap manager using a byte array
signed ints as block header and footer
+ve == free
-ve == allocated