Add partial support for 8-bit loads

We're big-endian.
when we have this in memory:

00 01 02 03

And we need the first byte, we load the first 16-bit word:

0x0001

The first byte is then in the upper part of the word, and requires
a right shift by 8.
So any load into an 8-bit typed container needs to shift stuff.

So far, stores from/to the stack are exempted, they always load/store
full 16-bit words.

And a few othe rminor things. Like string null terminators.
And escaped characters in character literals.

Can you believe it's spelled 'literal', with a single t?
Me neither.

cpu/cpu.vhdl

@@ -121,7 +121,11 @@ begin
         end if;
 
         regn_0 := to_integer(unsigned(load_reg(3 downto 0)));
-        reg_d(regn_0) <= mem_in;
+        if load_addr(0) = '1' then  -- 8-bit load
+          reg_d(regn_0) <= mem_in(7 downto 0) & x"00";
+        else
+          reg_d(regn_0) <= mem_in;
+        end if;
       when BRANCH =>
         inst := x"0000";  -- NOP
         reg_d(14) <= std_logic_vector(unsigned(reg_q(14)) + 2);