Slightly improve the C and C++ support. Allow for function return

Slightly improve the C and C++ support.  Allow for function return
types being on the same line as the function name, this finally closes
PR # bin/1785.  Also allow :: and ~ as part of the function name, for
C++.

Still, C++ operator overloading will not be recognized as a valid
function name.  Fixing this would require a major overhaul of the \p
recognition parser.