implement most bit-* on integers

unsigned-bit-shift-right is missing, but the others are there.
add bit-and-not for completeness
add pos?, neg? and zero?
add aget, aset and make-array
add alength for completeness
add aslice and aconcat

i'm not really happy with adding all these, but maybe they are useful to
allow writing faster low-level code in pixie.
fix aslice with negative integer arguments
Merge pull request #39 from heyLu/bitops-and-arrays

Bitops and arrays
reading stdlib now happens at runtime
more work on async-io
some cleanup
Merge branch 'master' into async-io