Improve how to redefine macros in 2012/endoh1 alt

Now one can use variables SLEEP, TIMER, GRAVITY, PRESSURE and VISCOSITY,
rather than single letter variables. This is like other commits where
instead of having to redefine CDEFINE one can do something like

    make clobber SLEEP=50 GRAVITY=I TIMER=15 alt

Notice that some can be set to I rather than a number. See the author's
remarks for details.

The try.alt.sh script was updated for this improvement.

2012/endoh1/README.md

@@ -59,7 +59,7 @@ for fun. That is controlled by the variable `A`; 0 disables it.
 If you wish to change the speed you should do:
 
 ```sh
-make clobber CDEFINE="-DS=N" alt
+make clobber SLEEP=N alt
 ```
 
 where `N` is number or the letter `I`.
@@ -75,7 +75,7 @@ you wish to change the viscosity and pressure factors but leave the other macros
 alone:
 
 ```sh
-make clobber CDEFINE="-DV=X -DP=Y" alt
+make clobber VISCOSITY=X PRESSURE=Y alt
 ```
 
 where `X` and `Y` are numbers or the letter `I` and which are, respectively, the
@@ -88,7 +88,7 @@ it from being done.
 If you want to disable the alarm time, set `A` to 0:
 
 ```sh
-make clobber CDEFINE="-DA=0" alt
+make clobber TIMER=0 alt
 ```
 
 It cannot be < 0 or > 60 (arbitrarily selected).
@@ -97,7 +97,7 @@ Try slowing down the display by increasing the sleep time from `12321` to
 `50000`:
 
 ```sh
-make clobber CDEFINE="-DS=50000" alt
+make clobber SLEEP=50000 alt
 ```
 
 Now try using both `endoh1.alt` and `endoh1_color.alt` as you would `endoh1` above.
@@ -106,7 +106,7 @@ Also try speeding up the display by decreasing the sleep time from `12321` to
 `9999`:
 
 ```sh
-make clobber CDEFINE="-DS=9999" alt2
+make clobber SLEEP=9999 alt2
 ```
 
 WARNING: again, be careful with too low a value if you're sensitive to flashing
@@ -119,13 +119,13 @@ instance:
 
 
 ```sh
-make clobber CDEFINE="-DG=5 -DP=5 -DV=5" alt
+make clobber GRAVITY=5 PRESSURE=5 VISCOSITY=5 alt
 ```
 
 You might try even:
 
 ```sh
-make clobber CDEFINE="-DG=I" alt
+make clobber GRAVITY=I alt
 ```
 
 See the author's remarks for details on these macros.