Log Message:
tex-incgraph{,-doc}: update to 1.2.0

### Added
- Option `overlay page number options`
- `\igrGetPageSize`
- `\igrPageWidth`
- `\igrPageHeight`
- `\igrSetPageSize`
- `\igrGetLastPage`
- `\igrLastPage`
- Adding/Guessing file name extensions
    - Option `extensions`
    - Option `extensions add`
    - Option `extensions from graphics`
    - Option `ignore on not found with extensions`
    - Option `ignore on not found with extensions*`
- Option `no existence check`

### Changed
- Changelog moved from CHANGES to CHANGES.md and adapted to
  [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
- From now on version numbers adhere to
  [Semantic Versioning](http://semver.org/spec/v2.0.0.html)
- Readme moved from README to README.md and adapted to
- Documentation code revised
- Internal package creation process modernized (invisible to the user)
- Adaption of paper size made compatible with lualatex
- Implementation of `\incgraph` and `\incmultigraph` changed (to LaTeX3)

### Fixed
- Documentation typos corrected
- `\incgraph` ignored option settings for not existing files.