Add shell redirections

[vinc]

The initial plan for MOROS Shell was to emulate redirections with pipes and read or write commands like print hello -> write /tmp/test that can be shortened to p hello > w /tmp/test where > is the equivalent of | for Unix shells.

Pipes are not yet implemented but with a DUP syscall and the file handle table it's easy to implement redirections like print hello => /tmp/test where => is the same than > for Unix shells.

[vinc]

For now only print hello => /tmp/test or print hello 1=> /tmp/test works while read <= /tmp/test for example wouldn't because reading from stdin is not implemented for most tools.