Fixes in 2018/yang

Update .gitignore with files created by the commands in the README.md
(and some that can be with the right combinations that are not noted).

Typo and formatting fixes in README.md.

2018/yang/.gitignore

@@ -4,9 +4,10 @@ generated3.c
 generated4.c
 generated5.c
 left
-msg0
-msg1
-msg2
+msg[0-9]
 prog
 right
 shift
+rotated_counterclockwise.txt
+rotated_clockwise.txt
+no_leading_space.txt