renamed test folder to examples and docs improvements

[StrikerRUS]

• Removed version from the title of the rgf-guide.rst file (we already have it in the readme);
• non-existent anchor link in the FastRGF readme file fix (6 -> 7);
• unified references by removing authors from the link part and by capitalizing titles;
• renamed RGF/test folder to RGF/examples for the consistency with FastRGF and rgf_python and because it's really examples but not tests;
• made snippets of the content of .inp files in rgf-readme.rst consistent with the original files (comments part);
• changes according to the new repo structure and test folder renaming;
• added links from rgf-guide.rst to described files (unfortunately, unlike .md format, .rst doesn't allow to decorate link as inline code piece).

[riejohnson]

Hi. I didn't check all the details, but I'm fine with what you're trying achieve. Thanks.