add support for RobotFramework .robot files

samples/RobotFramework/keyword_driven.robot

@@ -0,0 +1,37 @@
+*** Settings ***
+Documentation     Example test cases using the keyword-driven testing approach.
+...
+...               All tests contain a workflow constructed from keywords in
+...               `CalculatorLibrary`. Creating new tests or editing existing
+...               is easy even for people without programming skills.
+...
+...               This kind of style works well for normal test automation.
+...               If also business people need to understand tests, using
+...               _gherkin_ style may work better.
+Library           CalculatorLibrary
+
+*** Test Cases ***
+Push button
+    Push button    1
+    Result should be    1
+
+Push multiple buttons
+    Push button    1
+    Push button    2
+    Result should be    12
+
+Simple calculation
+    Push button    1
+    Push button    +
+    Push button    2
+    Push button    =
+    Result should be    3
+
+Longer calculation
+    Push buttons    5 + 4 - 3 * 2 / 1 =
+    Result should be    3
+
+Clear
+    Push button    1
+    Push button    C
+    Result should be    ${EMPTY}    # ${EMPTY} is a built-in variable