Fix minor error in the man page

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Fix typo in HACKING.md

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Add support for custom transition start and end

Signed-off-by: Mattias Andrée <maandree@operamail.com>
merge customisable-elevations and fix trivial merge conflict

Signed-off-by: Mattias Andrée <maandree@operamail.com>
update readme

Signed-off-by: Mattias Andrée <maandree@operamail.com>