malloc.read needs offset and size

[yegor256]

Currently, malloc.read reads the entire memory block, which is not effective. Let's make it read from offset provided and only the size of bytes.

(malloc 1024).pointer > p
p.write 100 "Hello!"
QQ.io.stdout
  (p.read 100 6).as-string

[yegor256]

@maxonfjvipon WDYT?

[maxonfjvipon]

@yegor256 sounds reasonable, let's do it