filesystem: a RAM FS (WRAMX) + ls/cat/save/rm; wc/head read files

- fs.asm: 8-slot RAM filesystem in WRAMX ($D000-$DFFF), name[8]+len[2]+data[502];
  syscalls open/close/getb/putb/list/remove, seeded with a 'readme' at boot.
- libc: open/close/fgetc/fputc/flist/fremove wrappers + O_READ/O_WRITE/NOFD.
- tools: ls, save (stdin->file, one line), rm; cat/wc/head now take a file arg.
- fix: syscall dispatch clobbers A, so putb takes its byte in E (was reading the
  handler's low address byte, 0xDC); ls NUL-terminates 8-char names.
- verified: save/cat/ls/rm cycle; wc readme -> '2 7 38'; head -n 1 readme.
- README: document the filesystem + the A-clobber ABI note.

1 files changed, 9 insertions, 0 deletions

diff --git a/c/ls.c b/c/ls.c
new file mode 100644
index 0000000..f7e5161
--- /dev/null
+++ b/c/ls.c
@@ -0,0 +1,9 @@
+#include "gbos.h"
+/* ls: list files in the RAM filesystem. */
+void main(void) {
+    char name[9];
+    unsigned char i;
+    for (i = 0; i < 8; i++) {
+        if (flist(i, name)) { name[8] = 0; puts(name); nl(); }
+    }
+}