Added given lab3 code
Copied .gitignore from lab2 branch
Untracked some autogenerated files
Created skeleton pipe syscalls and main test program

Added pipid32 type to kernel.h
Defined NPIPE, PIPE_SIZE, PIPE_{FREE,USED,CONNECTED}, and pipe_entry struct in pipe.h
Added pip{create,delete,connect,disconnect,write,read} syscalls to the list in prototypes.h
Added pipe.h to the list of included files in xinu.h
Added pip{create,delete,connect,disconnect,write,read} to the list of C files to be compiled in Makerules
Defined pipe_table in initialize.c
Created a main test program which connects a producer to a consumer using a pipe
Created skeleton pipe system call files
Added pipe state, buffer, and read/write semaphores
Initialized pipes
Implemented pipecreate
Added isbadpipe macro
Implemented pipdelete
Remembered to restore interrupts after deleting a pipe
Implemented pipconnect
Accessed pipe by reference in pipe table instead of a copy
Implemented pipdisconnect
Decided to use head index and length instead of head and tail pointers
Swapped reader/writer in pipconnect
Renamed pipconnect ends to be more clear
Merge branch 'lab3'