Previously we were showing filenames together with function names
when generating reports at function granularity. This was an attempt
to provide more information to the user, but it clutters the output.
Also, in cases where a function is associated to multiple files
(eg template instantiations in C++), keeping the filename may prevent
us from combining nodes from the same function.

Will stop keeping filenames at the default function granularity, and will
remove the "functionnameonly" option which was previously providing this
functionality.

There is a check to only honor the call_tree option when generating non-visual
reports, but it wasn't being checked in all appropriate places, causing a
mismatch that triggered a panic.

Also update the build instructions to use go get