Added new capability to the `%load` magic to search the user's namespace for modules, classes, or functions and inspects those to load source.

Currently, the `-n` argument must be passed to `%load` to enable this capability.
Reworking object look up code to use existing inspect functionality.
Added docs for new load magic functionality
Merge pull request #5650 from titsworth/load_from_namespace

Expanded %load functionality - user namespace search