#229 build example code and use output

[fktn-k]

This PR has added the docs/examples directory to gurantee the example codes and their outputs by actually building/running the codes before publishment.
Along the way, some misimplementation in the example codes were found and have been fixed.

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Pull Request Checklist

Read the CONTRIBUTING.md file for detailed information.

• [x] Changes are described in the pull request or in a referenced issue.
• [x] The test suite compiles and runs without any error.
• [x] The code coverage on your branch is 100%.
• [x] The documentation is updated if you added/changed a feature.

Please don't

• The C++11 support varies between different compilers and versions. Please note the list of supported compilers. Some compilers like GCC 4.7 (and earlier), Clang 3.3 (and earlier), or Microsoft Visual Studio 13.0 and earlier are known not to work due to missing or incomplete C++11 support. Please refrain from proposing changes that work around these compiler's limitations with #ifdefs or other means.
• Please refrain from proposing changes that would break YAML specifications. If you propose a conformant extension of YAML to be supported by the library, please motivate this extension.
• Please do not open pull requests that address multiple issues.

[coveralls]

coverage: 100.0%. remained the same when pulling 1de80ff4943a3a0a90da6dfceaa6151cdf89d133 on feature/229_build_example_code_and_use_output into d53395e3baeb36b68f4e1f89dcef04db2ef5d30a on develop.