Mostly cosmetic changes to simulator
Simulation: Change how simulated UART data availability is signaled.  The last change is not safe (but I don't like this workaround either -- maybe something better will come to me).
Cosmetic update to comments/README
Update TODO list
Add support for 64-bit lonjmp/setjmp in simulator platform
Update ChangeLog
configs/sim/nsh/defconfig -- refresh, enable wall-time, dow builds natively in 64-bit mode
Update README
Update To-Do list
Fix build error with CONFIG_SYSTEM_TIME64
Update TODO list + cosmetic changes to clock_systimer.c
fix reversed in/out file closing when an error occurs.  From Ken Pettit
Update ChangeLog
Implement creat() as a macro
Add pread() and pwrite()
Add pread(0 and pwrite() system calls
Update ChangeLog and ToDo
First pread/pwrite typo fixes
Update user guide
Add aio.h header file