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/Lexer.cpp

@@ -21,6 +21,8 @@ BAN::ErrorOr<BAN::Vector<Token>> tokenize_string(BAN::StringView string)
 				case ')':  return Token::Type::CloseParen;
 				case '$':  return Token::Type::Dollar;
 				case '"':  return Token::Type::DoubleQuote;
+				case '>':  return Token::Type::GreaterThan;
+				case '<':  return Token::Type::LessThan;
 				case '{':  return Token::Type::OpenCurly;
 				case '(':  return Token::Type::OpenParen;
 				case '|':  return Token::Type::Pipe;