1.Description of the program
----------------------------
The purpose of this (last!) programming assignment is more of an emphasis on C systems­
level programming along with more Standard C Library routines. It will build a limited
version of the ls utility that we can call mylsthat will implement a small subset of
ls options (­a, ­l, ­t, and ­r or ­altr). It can supply myls with any combination of 
files and directories (directories are not searched recursively by default this will
be an extra credit option).


2.Compile it
---------------------------
Just typeing "make"


3.Run it
---------------------------
After compiling the programing,you can run it by typeing:
./myls : display all the file in the current directory
./myls 'filename' : display all the file in 'filename'
./myls -l 'filename' : display detail information of all the file in 'filename' 
./myls -t 'filename' : display all the file in the order of modifytime in 'filename'
./myls -r 'filename' : display all the file in the order of name in 'filename'
./muls -a 'filename' : display all the file in 'filename'


4.An example of output
----------------------------
When all the input is right, the output will be the list of filename.


5.An example of error output
----------------------------
If the input is wrong, like the form is wrong, the output will be error output.


6.Test
----------------------------
All the test is right.


7.More information
---------------------------
If you don't want to read more, all you need to do is typeing "make" and typeing
command in item "3.Run it". Affter that, you can typeing "make clean" to remove
the file: myls,myls.o.