The current way to highlight TODOs is `spacemacs/highlight-TODO-words`
which is a spacemacs' hard-coded function.
This commit changes it for the `hl-todo` package. This imply:
- More keywords are supported out of the box.
- Keywords are associated to faces, so they are shown in different
colors.
- Keywords are stored with their faces in a list, so it's easier for
users to add their own keywords and faces (as contrary to a regexp).
- It is possible to disable highlighting by simply excluding the
package.
I feel that it is not needed because it makes not a lot of sense to
have it non global since it is a dotfile variable.
Also remove ' from the docstring for consistency.
`global-linum-mode` is making line numbers appearing in `*spacemacs*`
and `helm` buffers, what is annoying.
This change make the linum `SPC t n` toggle buffer-local, and add a
customization variable in `.spacemacs` to enable line numbers globally.
«Globally» here as to be understood as «in `prog-mode` and `text-mode`».
