Added rudimentary keyboard polling

src/example/char_in.asm

@@ -0,0 +1,13 @@
+10;Queries the keyboard for input and prints the resulting keycode
+20          ORG     100H        ;Tell the assembler to start at addr 0x100
+30START:    LD      HL,GREET    ;Load the start addr. of the banner text
+40          LD      B,15H       ;The length if the string
+50          LD      DE,0H       ;Start output in the top left corner
+60          CALL    84CDH       ;Call str_out
+70LOOP:     CALL    8881H       ;Call the char_in
+80          LD      DE,16H      ;Position cursor in row 0, col 22
+90          CALL    8468H       ;Print the char
+100         JR      LOOP        ;Retrun to the loop
+110         RET                 ;End the program
+120GREET:   DB      'Test keyboard input: ' 
+130         END                 ;Mark the end of code for the assembler