Create STYLE_GUIDE.md

[JafarAbdi]

Description

Please explain the changes you made, including a reference to the related issue if applicable

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extended the tutorials / documentation, if necessary reference
• Include a screenshot if changing a GUI
• Document API changes relevant to the user in the moveit/MIGRATION.md notes
• Created tests, which fail without this PR reference
• Decide if this should be cherry-picked to other current ROS branches
• While waiting for someone to review your request, please consider reviewing another open pull request to support the maintainers

[henningkayser]

@JafarAbdi Could you add that LOGGER should be inside the namespace by default? Also, we need to specify how loggers can be used in header files (there are some cases).

[JafarAbdi]

@JafarAbdi Could you add that LOGGER should be inside the namespace by default? Also, we need to specify how loggers can be used in header files (there are some cases).

@henningkayser Adding loggers to header files could violate the one definition rule (for example two header files with the same namespace adding the logger to both headers will cause an error), do you mind sharing some cases so I could document them .?

[rhaschke]

Adding loggers to header files could violate the one definition rule

For this reason, I suggest using a static const class variable named LOGGER, which then could be used/referenced from the header as well.

[JafarAbdi]

@henningkayser Some libraries just contain one source file, the current style will duplicate the name .? for example lma_kinematics_plugin

Should the logger name be moveit_lma_kinematics_plugin.lma_kinematics_plugin .? shouldn't lma_kinematics_plugin be sufficient .?