Add 'jumpIf' and 'jumpIfNot' commands to README and executor; implement parsing, execution, and linter support for conditional command jumps in test scripts.

README.md

@@ -103,6 +103,20 @@ sleep 2500 "waiting for animation"
 sleep 500 "let page settle"
 ```
 
+#### jumpIf
+Jump over a specified number of commands if an element exists:
+```
+jumpIf element=span childText="Server-Warenkorb" jump=4
+jumpIf element=div id="error-message" jump=2
+```
+
+#### jumpIfNot
+Jump over a specified number of commands if an element doesn't exist:
+```
+jumpIfNot element=span childText="Server-Warenkorb" jump=4
+jumpIfNot element=div id="success-message" jump=2
+```
+
 ### Element Selectors
 
 You can combine multiple attributes: