This was required, as clang-7 formatted code leads to
`compound-token-split-by-space` warning in clang-12.

- new exceptions based on clapp::exception::clapp_exception.
- added `parse_and_validate()` function.
- added found-func
- added help-option
- added more constexpr
- added more comments to examples
- code cleanup
- bump version t0 0.1.0
- added gitlab-ci pipeline
- added double/float values
- added support for vector of short/long options
- added doc-extractor