Test for the example in CI

It would be nice if there is a CI tester (such as Travis CI) for the examples in the user guide.
Such a scheme can keep the examples runnable for each commit.

Here is the list to solve this issue:
- [x] [cwltest] [cwltest/#38](https://github.com/common-workflow-language/cwltest/pull/38) add support for "known failure" tests
- [X] [user_guide] make the examples in each section independent
- [X] #43 Categorize the examples for each section
- [x] #51 Add files for the examles in user guide
- [ ] [user_guide] add conformance test for the examples
- [x] #52 Add conformance test for section 4 using cwltest
- [x] #61 Add tests for the examples
- a conformance test for section 11 (1st example)
- conformance tests for section 2, 3
- [x] Add conformance tests for section ~7~, ~9~, 11 (2nd and 3rd examples), 12, 13 and 14
- [x] #92 for section 7
- [x] #94 for section 9
- [x] #98 for section 11
- [x] #99 for section 12
- [x] #100 for section 13
- [x] #101 for section 14
- [ ] Add conformance tests for section 19 and 20
- [x] #102 for section 19
- [ ] add PR for section 20 (now 19: software requirements)
- [ ] add PR for section 22 (scatter)
- [x] [user_guide] add files for CI for the examples
- [X] #53 Add .travis.yml to test the examples
- [x] #55 Enable conformance test with Travis CI