Request for OSCLI call to be added to bbc_kernal.mfk

I thought it might be useful to add this OSCLI call to bbc_kernal.mfk
as an example.

```
// OSCLI. Send a string to command line
// Input: X = Lo Byte of address of command string ($0D terminated)
// Y = Hi Byte of address of command string ($0D terminated)
asm void oscli(word register(xy) cmd) @$FFF7 extern

```

Can be called using a string array or a string directly

```
array oscli_cat = "*.{x0D}" // Display disk directory catalog

[ in main() ]

oscli( oscli_cat )

oscli( "*TYPE !BOOT{x0D}" )

```

Assembles as

```
;
;line:47:hello_world_extended.mfk
; oscli( oscli_cat )
LDY #hi(oscli_cat.array)
LDX #lo(oscli_cat.array)
JSR $FFF7
;
;line:49:hello_world_extended.mfk
; oscli( "*TYPE !BOOT{x0D}" )
LDY #hi(textliteral$2a545950452021424f4f540d.array)
LDX #lo(textliteral$2a545950452021424f4f540d.array)
JSR $FFF7

```

Thank you for your great work creating and maintaining the Millfork repository 👍

Regards,

Derek.