Implement rules from emacs style guide

[Fuco1]

https://github.com/bbatsov/emacs-lisp-style-guide

For inspiration look at https://github.com/Fuco1/Elsa/blob/master/elsa-ruleset.el the ruleset elsa-ruleset-style contains the style rules.

These are in turn defined in https://github.com/Fuco1/Elsa/blob/master/elsa-rules-list.el.

The naming of these files isn't great and I think we will need to split it apart better, somewhat in style of the extension and typed... so we will have elsa-ruleset-style.el which will define the ruleset and all the accompanying rules.

• [ ] Syntax
  • [x] Don't wrap the else clause in progn
  • [x] Use when instead of (if .. (progn ...))
  • [ ] Use unless instead of (when (not ...))
  • [ ] Use t as catch-all in cond forms
• [ ] Naming
  • [x] Use lisp-case
  • [ ] Use project prefix (how to detect this?)
  • [ ] Use _ prefix for unused lexical variables
  • [ ] Use -- for private functions (see #26, if there is no reference maybe it is public API and should not be private)
  • [ ] Face names don't end in -face
• [ ] Functions
  • [ ] No lambda for hooks or settings
  • [ ] Don't quote lambda forms with '
  • [x] Don't wrap functions in lambdas
  • [ ] Use #' for quoting of functions

[Fuco1]

We can also look at the closure version https://github.com/bbatsov/clojure-style-guide some of the things might be relevant.