Added io.Reader and io.Writer helper functions for loading/storing
Added two more utility functions

LoadFile: Similar to LoadReader, but instead takes a filepath to read from.
SaveFile: Similar to SaveWriter, but instead takes a filepath to write to.
Changed API slightly

AddSub now takes a Configer rather than a *Config. The *Config version
is now named AddSubConf. AddSub was added because it should not be
required to keep track of *Config's in user code.

AddSub and AddSubConf both now return an error instead of a *Config, equal
named sub-configurations are now disallowed and will return an error from
both of these functions.
Added a cycling go->marshal->go test case

And fixes a typo found by this test case in the utility functions