Fix title image in readme
Fixes #224 jedi does not need to be installed manually

in README
Temporarily comment the command prefixes for JS layer
Fix incorrect example for evil-escape-key-sequence

When I followed the example in the documentation, `describe-variable` reflected the updated value ("jj") but spacemacs ignored it and continued to use the default value ("fd").

`evil-escape.el` mentions:

```elisp
;; The key sequence can be customized with the variable
;; `evil-escape-key-sequence'
;; It must be set before requiring evil-escape.
```

So I tried moving the `setq` to `/init` instead of `/config`. That worked.
Clarification about unsupported `jj`, and `jk` sequences

to escape states and buffers in DOCUMENTATION
Update conventions for tests and REPLs
Update ESS key bindings according to conventions
Update Python key bindings according to conventions
Add convention for code navigation and documentation
Add achievement for 100th PR
Refactor python layer to be more modular
Comment function spacemacs/declare-prefix-for-mode

Not working nicely with guide-key for now.