Added undocumented(), undefined(), isdeprecated(); doc and export updates.

* undefined(m::Module): list the undefined methods in a module
* undocumented(), undocumented_by_file(), undocumented_rst(): produce a list of undocumented methods in various formats
* current_module(): return the current_module() (is this always Main?)
* isdeprecated(fn): true if fn is deprecated
* commented out undefined functions in exports.jl (these could probably be removed)
* documentation fixes (in manual) and update