usr: grep, more, cp, nc - and make pollcon pump the link

The shell has had pipes for a while with nothing to pipe *through*, and
an 18-row screen with no way to stop output scrolling off it.

- grep [-vin] PAT [file]: substring match (no regex), stdin or a file,
  grep(1)'s exit convention. The other end of the pipe, at last.
- more [file]: pages 17 lines at a time, --More-- bar in white-on-blue,
  any key pages, q quits. Counts *screen* rows, so wrapped lines pay
  their real cost. Keys come from pollin/pollcon, not stdin, so
  `cat big | more` still has a keyboard.
- cp SRC DST: the fs has rm/mkdir but no way to duplicate a file. mv is
  this plus rm (there is no rename). Rejects SRC == DST, which would
  otherwise truncate the source via O_WRITE before reading a byte.
- nc [-s] HOST PORT: raw TCP. Interactive (START sends the line with a
  CRLF, /q quits) or -s to pump stdin and print the reply with its own
  wall-clock idle timeout, because the kernel's blocking recv counts
  pumps, not seconds. Generalizes what chat/irc hardcode:
  `nc towel.blinkenlights.nl 23` works.

sys_pollcon now pumps the link before draining the console ring. The
ring is filled *by* net_pump, so a program that never touches the
network polled a ring nothing would ever fill: host-injected keys
(gbtype/gbdemo) hung `more` forever, and the Game Boy stopped answering
pings for as long as it ran. KGetc already pumps for this reason.

New tools take banks 35-38. Locals over statics in all four: a program's
_DATA starts at $A000, where the shell leaves the command line.

1 files changed, 9 insertions, 6 deletions

diff --git a/README.md b/README.md
index 6d0061a..95bc362 100644
--- a/README.md
+++ b/README.md
@@ -17,12 +17,15 @@ into the on-screen console. Regenerate it anytime with `tools/gbdemo` (below).*
   background jobs (`spin &`), `ps`, `kill` — round-robin cooperative
   scheduling across banked memory with an HRAM context switch.
 - **A shell** (written in C, running *on* the GB) with I/O redirection
-  (`>` `<`) and pipes (`|`), argument passing, and a cwd-aware prompt.
+  (`>` `<`) and pipes (`|`), argument passing, and a cwd-aware prompt — with
+  `grep` to put on the other end of the pipe, and `more` to page anything
+  longer than the 18-row screen.
 - **Networking, for real**: the kernel owns SLIP over the link port, IPv4,
   ICMP, UDP and TCP; userland gets BSD-ish sockets via one syscall. On top:
   `dhcp` (boot-time lease), `ping`, `nslookup` (real DNS), `wget` (HTTP),
-  `chat`, and a colorized **IRC client** (`irc HOST [NICK]`, `/join` and
-  friends, SELECT for the keyboard).
+  `nc` (netcat: `nc HOST PORT` interactively, or `nc -s HOST PORT < file` to
+  pipe a request in and print the reply), `chat`, and a colorized **IRC
+  client** (`irc HOST [NICK]`, `/join` and friends, SELECT for the keyboard).
 - **A network to plug into**: `tools/gbhub` is a virtual switch + DHCP server +
   NAT gateway — spawn a fleet of Game Boys that ping *each other* and reach
   the real internet; `tools/gbjoin` attaches an interactive GB to it, and
@@ -31,9 +34,9 @@ into the on-screen console. Regenerate it anytime with `tools/gbdemo` (below).*
   colors) + an **on-screen keyboard** on the window layer (SELECT toggles it).
 - **Persistent filesystem** on battery-backed cart RAM: inodes, nested
   directories, per-process cwd — survives power-off.
-- **A C toolchain**: userland is plain C compiled with SDCC (`sm83`); ~30
-  tools ship in `usr/` (`cat`, `wc`, `head`, `ls`, `uptime`, …). Adding a
-  program is one `.c` file + a table entry.
+- **A C toolchain**: userland is plain C compiled with SDCC (`sm83`); ~35
+  tools ship in `usr/` (`cat`, `wc`, `head`, `grep`, `cp`, `more`, `ls`,
+  `uptime`, …). Adding a program is one `.c` file + a table entry.
 
 ## Quick start