libc + CLI tools: a small C userland

- libc: add putc, puts, strlen, getargs (args string), EOF (=4) for readc.
- args: shell splits the command line at the first space ("cmd\0args\0" at
  $A000, inherited by the child via fork); getargs() returns the arg string.
- shell: exit on Ctrl-D/EOF; $ prompt over a clean read loop.
- tools (c/): echo (argv), cat (stdin->stdout to EOF), uname, pid (decimal
  print), true, false. Each built to a ROM-bank blob and registered.
- Makefile: CBLOBS list builds all C programs.
- README: document libc + the tool set.

1 files changed, 10 insertions, 0 deletions

diff --git a/c/cat.c b/c/cat.c
new file mode 100644
index 0000000..4092778
--- /dev/null
+++ b/c/cat.c
@@ -0,0 +1,10 @@
+#include "gbos.h"
+/* cat: copy stdin to stdout until EOF (Ctrl-D / pipe end). */
+void main(void) {
+    char c;
+    for (;;) {
+        c = readc();
+        if (c == EOF) break;
+        putc(c);
+    }
+}