Implemented the 'help' builtin, and support for :h <topic> in ex mode

:h is an alias for the 'help' builtin.

'help' takes a single argument and tries to find a suitable match among the files in '$SHED_HPATH'

if a match is found, this file is opened in your pager

calling the 'help' builtin using :h in ex mode will preserve your current pending line

src/procio.rs

@@ -115,6 +115,11 @@ impl IoMode {
   pub fn buffer(tgt_fd: RawFd, buf: String, flags: TkFlags) -> ShResult<Self> {
     Ok(Self::Buffer { tgt_fd, buf, flags })
   }
+	pub fn loaded_pipe(tgt_fd: RawFd, buf: &[u8]) -> ShResult<Self> {
+		let (rpipe, wpipe) = nix::unistd::pipe()?;
+		write(wpipe, buf)?;
+		Ok(Self::Pipe { tgt_fd, pipe: rpipe.into() })
+	}
   pub fn get_pipes() -> (Self, Self) {
     let (rpipe, wpipe) = nix::unistd::pipe2(OFlag::O_CLOEXEC).unwrap();
     (