Shell: Implement redirections

This works well enough. At the moment redirections can appear anywhere
in the command **after** environment variables and possible alias
command. This means commands like `>foo echo hello` are not supported.
I don't think this is big enough problem for now (99% time redirections
are given after arguments) that i would rewrite the environment and
alias parsing.

userspace/programs/Shell/TokenParser.h

@@ -44,6 +44,8 @@ private:
 	BAN::ErrorOr<CommandArgument::ArgumentPart> parse_single_quote();
 	BAN::ErrorOr<CommandArgument> parse_argument();
 
+	BAN::ErrorOr<SingleCommand::Redirection> parse_redirection();
+
 	BAN::ErrorOr<SingleCommand> parse_single_command();
 	BAN::ErrorOr<PipedCommand> parse_piped_command();
 	BAN::ErrorOr<CommandTree> parse_command_tree();