Merge pull request #1484 from matthiasbeyer/prepare-0.8.0

Prepare for 0.8.0
Add changelog for 0.8.0
Merge pull request #1483 from matthiasbeyer/readme-vacation-notice

Readme vacation notice
Add github pull request/issue template
Add vacation notice
Merge pull request #1482 from matthiasbeyer/libimagrt/cli-validation

libimagrt: cli validation
Add CLI validators in default CLI setup
Update help, clap does the rest here
Merge pull request #1481 from matthiasbeyer/imag-category/init

imag-category: Initial import
imag-category: Initial import
Add functionality to remove categories
Merge pull request #1468 from matthiasbeyer/imag-ids/filters

imag-ids: filters
Add trace output in filtering process
Add language documentation in commandline help
Add store cache flushing after each 100st entry
Implement header filter language
Implement 'where' subcommand
Add notes how the filter language should look like
Move collection filter to new module