convert mode/paste/iminsert parts to function names.
convert branch/hunks/bufferline to function names.
convert the rest to use define section.
automatic separators.
introduce parts metadata.
move init code into new file, add section.
fix indentation.
check existence of all variables.
define the rest of the extensions.
use correct direction of separators.
basic tests and travis integration.
test some commands
test creation of sections
add tests for the builder
test util functions
test the layout config for the default extension.
support for prefixing with a highlight group.
define default statusline items with empty contents.
more compatible test for older vim version.
separators unnecessary in warning section.