Replace swank with micros

[cxxxr]

Overview

This change corresponds to phase 1 and phase 2 of #688

I have replaced the part where I was using the swank package in lisp-mode with micros.
In addition, I had bundled micros, but have now switched it to a submodule.

Breaking change

Due to this change, it is no longer possible to connect to Swank.
Instead, we will use micros, and there are currently no differences in the API.

;; before
(swank:create-server :dont-close t :port <port-number>)

;; after
(micros:create-server :dont-close t :port <port-number>)

In addition, since I have added micros as a submodule, updating the submodule is necessary.

$ git submodule update --recursive

[vindarel]

Note for devs who had cloned Lem before, I needed:

git submodule update --init submodules/micros

thx