Add directory support to userspace

[vinc]

• Create dirs from userspace
• Delete dirs from userspace
• Read dirs from userspace
• Add delete syscall
• Add /dev/null
• Add proc command
• Rename stat syscall to info
• Rename FileStat struct to FileInfo

[vinc]

The following pages were interesting when implementing the read syscall for directories:

• https://www.bo-yang.net/2011/03/07/plan9-intro-note-4
• http://man.cat-v.org/plan_9/5/read

In MOROS the stat syscall on a file or a directory returns the file attributes (called FileStat) that is a subset of its directory entry for userspace programs. The read syscall on a directory returns the same structure for each entry until its buffer cannot fit the next entry.

[vinc]

Rename stat syscall and FileStat to info and FileInfo.