Add function to get the next name of file in the romfs
Add function to get all the name of files
1.This function will return the number of files.
2.This function will store all name into a buffer and use '\0' to express the end of name.
Use enum to specify the type of commands
Add function to process the command ls
It can't get the correct name of files now.
Modify getNextFileName function
when it isn't have the next file, it will reutrn NULL