Remove obsolete Code
Add Check against null Values in context, so that there is no
accidential match because we add a null value to the Jacket list in
certain cases.
Do something against the Deprication Warning: "The return value of
index() will change from "false" to "null" in future versions of Sass.
For compatibility, avoid using "== false" on the return value. For
example, instead of "@if index(...) == false", just write
"@if not index(...)".
Remove redundancy in code checking for matching Contexts in the Jacket
Variable to prevent mistakes.
The Check "If jacket is a single context and selector list,
encapsulate." was only done in the Mixin but not in 
the Function.
rename function from "jacketMatch" to "jacket-match"
new function jacket-add-contexts
To add a context to an existing Jacket Variable was not easy to not
destroy the consistency of the list. Therefor I created this function.
new function jacket-else($value, $else, $contexts...)
It will return $value if the $contexts match or $else if not.
DEBUG, make all this work flawlessly, those Lists are hard to handle
Update documentation