Added a 'hello world' program

src/HELLO.ASM

@@ -0,0 +1,39 @@
+; This is an example of the Hello, World program.
+; This will define a function to print a string on the screen.
+; Uses 8080 assembler mnemonics.
+		ORG 100H         ; CPM programs start address
+		JMP START        ; go to program start
+; Variable storage space.
+MsgStr: DB 13,10,'Hello, world.',13,10,0
+Stack:  DW 0             ; place to save the old stack
+SBOT:   DS 32            ; reserve a local stack
+; Constants
+STOP:   EQU $-1          ; top of our stack
+BDOS:   EQU 5            ; adress of the BDOS call 
+; Start of the code segment
+; PRINTF: Prints a string on the screen using a BDOS function. 
+; The address of the string is expected to be in register HL.
+PRINTF:
+PRLOOP: MOV A, M         ; read next char
+		ORA A            ; check, if string has ended
+		JZ  PREND        ; if char == 0, then leave the loop
+		MOV E, A         ; load the char into E
+		MVI C, 2         ; load BDOS function id 2 into C
+		PUSH H           ; save the HL register
+		CALL BDOS        ; call the BDOS function
+		POP H            ; restore the HL register
+		INX H            ; point to the next char
+		JMP PRLOOP       ; do the next char
+PREND:  RET              ; return from subroutine
+; Start of the main code block
+START:  LXI H, 0         ; blank out HL
+		DAD SP           ; HL = SP
+		SHLD Stack       ; save the original stack
+		LXI H, STOP      ; set HL to the new stack top
+		SPHL             ; set SP to point to our new stack
+		LXI H, MsgStr    ; load the string addr into HL
+		CALL PRINTF      ; call our self defined print routine
+		LHLD Stack       ; load original stack addr into HL
+		SPHL             ; restore the original stack
+		RET              ; return control back to CP/M
+		END