Added "Function Navigator…" menu item

To make accessing the list of functions defined in the current source
file more discoverable a menu item has been added to the right-click
context menu which is the equivalent of "Super+R"
Added *.swp
Improved syntax detection

The detection of function definitions has been extended to cover both
styles of Lua function definitions:

     function f () body end

and

     f = function () body end

This improves the list of functions displayed by Super+R in particular.
Improved documentation lookup

Documentation lookup has been made smarter so that it displays the
correct page more often.  If it can't display a particular page it now
defaults to searching either the online Lua documentation or the Corona
SDK documentation depending on context.
Updated README