Add loader/arch/README
Rename arch_setup_stack() => setupStack()

(Coding style)
stkget() and stkfree():  Clarify documentation
system/create.c:  Remove redundant store to thrptr->stkptr
setupStack():  Fix stack alignment on ARM and MIPS

Ensure the stack is always 8-byte aligned when a new thread begins its
starting procedure.
shell:  Replace strncmp() with strcmp() where safe

This eliminates the need to manually count the characters in string
literals being compared against.  This also fixes bugs in several places
where the previous code forgot to count the null terminator and actually
tested for the prefix property rather than the equality property.
Update and reorganize docs/

- Organize the documentation exported from the Embedded Xinu Wiki into
  arm/, development/, features/, mips/, projects/, and teaching/
  directories.

- Delete a few unneeded documentation files, such as those for accessing
  the (now deprecated) Subversion repo

- Fix many links and tables

- Add page about BCM2835 memory barriers

- Add page about SMSC9512 using info previously in
  device/smsc9512/Doxygroup.c

- Replace Standard Library page using info previously in
  lib/libxc/Doxygroup.c

- Improvements to various pages, such as ARP, Shell.

NOTE: Files under docs/mips/ and docs/projects/ still need work and there
should be a later commit handling them.