`.lpy` extension support

[ikappaki]

Hi,

I would like to add Basillisp file extension, .lpy, to the list of supported clojure-mode extensions.

This is just to get minimal support, there are some additional, specific to Basilisp, that can be declared for syntax highlighting, but will add them at later time.

PR to follow.

Thanks

[bbatsov]

Sure! Seems like a cool project, btw!

[bbatsov]

Closed by #676.