REQUEST: Support for C++ Documentation

[pjeschba]

This might be able to be added through the usage of cppman:

https://github.com/aitjcize/cppman

[powerman]

I'm not using C++, so it's hard to me to test is it works. But if you'll make PR using one of existing plugins as example - I'll be happy to merge or help you with vim-specific issues.