Reorganized directory structure, mostly to put all the interfaces in

Reorganized directory structure, mostly to put all the interfaces in
one place and make things clearer to the uninitiated.  Here's my
current understanding:

.
|-- libbe          (the guts of BE)
|-- becommands     (plugins for all "be *" commands)
|-- doc            (documentation, currently just the man page)
|-- interfaces     (non-commandline interface implementations)
|   |-- web
|   |   |-- Bugs-Everywhere-Web    (in Turbogears)
|   |-- gui
|   |   |-- beg    (in Tkinter)
|   |   `-- wxbe   (in WX)
|   |-- email
|   `-- xml        (xml <-> whatever conversion)
`-- misc           (random odds and ends)
    `-- completion (shell completion scripts)

Note that I haven't attempted to use the web or gui interfaces in a
while, so I'm not sure how well they're holding vs the core
development.