Now that the common configuration objects and session objects are part
of a public API, they need to be documented in a way that can be read
with godoc. This commit should lead to easier development with FRP as a
library.
The ClientCommonConf, configuration file path, and server UDP port are
now passed around as arguments instead of being shared between
components as global variables. This allows for multiple clients to
exist in the same process, and allows client.Session to be used as a
library more easily.
This option allows users to specify where they want assets to be loaded
from, like the "assets_dir" option that already exists for frps. This
allows library users to use the admin panel without having to bundle
assets with statik.
