now we support bitmap and buddy allocator for page

doc: add targets in doc/target.md
add run_test app to run all tests
fix error about brk syscall

1. add simple clone support, we ignore some arguments.
2. cargo fmt

handle the page fault

speed up compilation

memory size is 256MB now

solve pagefault for dbfs
update hugewrite file size

1. return ok in mount now
TODO: devfs in rvfs

fix error about syscall define

1. update page-table to support brk
2. update userlib allocator,now it uses sbrk

fix: fix bugs about lock -- disable interrupt
test: add test from rcore

The uart still has some bugs.

The kernel needs to modify many system calls to meet the requirements of
linux, and the user library needs to be corrected.
1. fix bugs about process switch
2. add syscall about time
3. support c app

add truncate/getdents syscall
fix bug about interrupt

remove extra blank lines

add basical functios about fs
fix some bugs
add some user app to test fs