rc: lisp: extracted custom slime hook for the sake of orthogonality
rc: lisp: reorganized for use-package

use-package with slime (and some other packages) doesn't achieve the
goal of deferring loadingslime package, as it basically loaded by
el-get already. However, it doesn't make sense to load it the old way
since we want to migrate to use-package everywhere, so it has been
done this way.
rc: browser: moved to use-package
rc: clients: partially moved to use-package
rc: completion: moved to use-package
updated todo
added custom keymap for orgmode