Moved struct definitions from internal header to respective headers

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Moved base initialization functions from internal to respective headers

 - Widget and canvas are supposed to be externally inherited
 - Moved widget and canvas base init to widget and canvas headers

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Added recursive widget children deletion

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Overhauled tab group widget to use widget tree

 - Tab group has tab widgets as children
 - Children list is used for tab rendering and selection
 - Custom structs and handling ported to widget functions

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Fixed "off by 11 error"

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Updated documentation

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Added strip for *nix build

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>