Separators by section (Left, Center, Right)

[SergioRibera]

This change adds the ability to have separators for each section in the statusline.

The custom deserializer is to allow these configuration variants.

separator = "؍" # All separators are set to this

# Only one is modified and the rest remains with the default value.
separator.center = "؍"

# All the following are modified
separator.left = "؍"
separator.center = "/"
separator.right = "|"