Add Bash & Batch scripts to run clang-format & amalgamation

[fktn-k]

This PR has added Bash and Batch scripts to run clang-format & amalgamation which are supposed to be run by myself and contributors.
Each 2 scripts whose names without file extensions (either .sh or .bat) are the same should behave in the same way as the other, respectively.
I intentionaly left the corresponding Make targets and made them just call the corresponding Bash scripts.
Since not all contributors can use Make, the related descriptions in the CONTRIBUTING.md have been updated to instruct them to run the Bash/Batch scripts.
I hope those scripts will make it more confortable for them to run Clang-Format and amalgamation.

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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.

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