initial checkin
remove a.out, accidentally added file
format code with Eclipse
tested initial release
format trap_asm.S
Merge branch 'master' of https://code.google.com/p/xv6-rpi
1. use 2-level page table for kernel heap, 2. clean up paging macros
save
save
integrate the buddy memory allocator
add .gitignore
detect the location of libgcc

Drop the original dependency of specific libgcc and use the cross
compiler to determine the correct location.
re-organize directory structure: separate device driver and lib

device specific implement is now moved to directory 'device':
  - PL190: Vectored Interrupt Controller
  - PL011: ARM PrimeCell UART
  - SP804: ARM dual-timer module

generic routine implementation is now moved to directory 'lib':
  - string functions
use CROSSCOMPILE instead of TOOLPREFIX since native compiler is used as well
detect host compiler
move mkfs to directory 'tools'
update .gitignore
improve build system to place object files into directory 'build'
add description text for 'make qemu' target