Improve the testing instructions on the README

See merge request redox-os/relibc!477

Document the test instructions and improve the title

See merge request !476

Implement pread and pwrite using the syscalls.

See merge request !475

Cleanup ld_so organization and move pthread_t into TCB

See merge request redox-os/relibc!474

Various futex fixes

See merge request !470

Fix double slashes in fpath.

See merge request redox-os/relibc!469

Add tests for unistd.h constants

See merge request redox-os/relibc!467

Protect fork() and clone() behind a rwlock.

See merge request redox-os/relibc!468

rlct_clone will acquire a read lock, whereas fork will acquire a write
lock. The write lock is necessary because the fork will clone the file
table, which would result in other threads' fork/clone file descriptors
not being closed. If an address space switch fd never gets closed, fork
child processes and new threads, may never switch address spaces before
they are started, which has resulted in hard-to-debug RIP=0 instr fetch
page faults.

Fix pthread rwlock code

See merge request redox-os/relibc!466

Don't map thread stacks as MAP_SHARED (lol), fix i686 signal trampoline

See merge request redox-os/relibc!465

MAP_SHARED means it will continue to be shared after forks, which
obviously isn't the correct behavior. `acid thread` doesn't segfault
infinitely, anymore.

Implement the event queue ABI.

See merge request redox-os/relibc!454

Implement new low-level signal trampoline

See merge request redox-os/relibc!460

Fix thread spawning on aarch64

See merge request redox-os/relibc!463

* Correctly align the stack
* Fix argument order of the ldp instructions
* Remove unnecessary ldr x5 instruction

Add tests for further sys/resource.h constants

See merge request redox-os/relibc!462

Add stub for SIOCATMARK command of ioctl.

See merge request redox-os/relibc!461