add image controller - for using images as cp/m disk

increase read buffer of UART from 16 to 64 bytes
allow selection of UART baud rate
allow selection of sd controller or image controller
update readme.md with more explanation of above and more detail on MultiComp use specifically for CP/M

Microcomputer6809Basic.vhd

@@ -22,6 +22,7 @@ entity Microcomputer6809Basic is
 	port(
 		N_RESET	   : in std_logic;
 		clk			: in std_logic;
+		baud_increment	: in std_logic_vector(15 downto 0);
 
 		sramData		: inout std_logic_vector(7 downto 0);
 		sramAddress	: out std_logic_vector(15 downto 0);
@@ -97,7 +98,7 @@ architecture struct of Microcomputer6809Basic is
 	signal n_interface2CS			: std_logic :='1';
 	signal n_sdCardCS					: std_logic :='1';
 
-	signal serialClkCount			: std_logic_vector(15 downto 0);
+   signal serialClkCount         : unsigned(15 downto 0);
 	signal cpuClkCount				: std_logic_vector(5 downto 0); 
 	signal sdClkCount					: std_logic_vector(5 downto 0); 	
 	signal cpuClock					: std_logic;
@@ -287,7 +288,7 @@ begin
 		-- 9600 201
 		-- 4800 101
 		-- 2400 50
-		serialClkCount <= serialClkCount + 2416;
+		serialClkCount <= serialClkCount + unsigned(baud_increment);
 	end if;
 end process;