Basic input and output

[mrsmkl]

Some of these already have initial implementations
3. Read
4. Write
5. Open
6. Close
41. Dup: just open with new descriptor
63. Dup2: what does it do?
140. Llseek
145. Readv
146. Writev
180. Pread64
181. Pwrite64
295. Openat
330. Dup3
333. Preadv
334. Pwrited