Improve documantion of many plugins
Specifically the configuration examples are now indented properly.
Improve perlpod formatting for multiple plugins
Escpecially the final marker ("=cut") was missing in these plugins.
Remove global flake8 override
[plugins/git/gitlab_statistics] added plugin to display GitLab stats
Graphs common GitLab statistics (user, repo, fork, ... count) using itsHTTP API statistics endpoint (requires a token to be set and passed tothe plugin)
Fixed user detection.The USER environment variable is not populated when the plugin is executed. Switched to checking the effective user.
Fixed error when using a user which doesn't have a default shell (like the default munin user on Debian/Ubuntu)
Added example graphs
Removed the use of the DEBUG environmant variable, kept only MUNIN_DEBUG
Changed the graph_category to file_transfer
Improved CONFIGURATION comment to better describe the user property
Fixed NOTES comment to better explain the fetch munin/cron modes
Renamed get_info to print_info
Improved the update methods : added the munin mode
Improved munin state file handling
Improved shell command generation to protect the injected configuration values
Improved how the statefile last modified date is updated
Improved configuration documentation
Misc code improvements
Added git_commit_behind
