Enhance general library documentation in keyword docs #924

The generated keyword documentation has generic part describing locator syntax, timeouts, etc. This is one of the first docs new users look so it is very important, but there are currently several issues with it:

• Not all functionality is adequately documented.
• Some features are documented in generic documentation part, others in library import section.
• Lot of the styles are messed up.
• New syntax features supported by Libdoc are not used.