Create snippets for doxygen commands

[rowanG077]

trafficstars

We are supporting doxygen commands with template generation but there are a lot more commands that can be generated and it would be really usefull to allow for some kind of intellisense when typing other commands.

So when type some configurable trigger then you get intellisense to add a doxygen command.

[cschlosser]

This could be more challenging then expected. This needs an completion provider for c/c++ comments.