separate responsibility

[ufcpp]

Now, ContextFreeTask has two responsibilities:

• await operations in the methods which return ContextFreeTask capture no context
• await operations on ContextFreeTask capture no context

These should be separated.

	used as a return type	used on await operators
ContextFreeTask	no	no
?	no	yes
?	yes	no
System.Threading.Tasks.Task	yes	yes

[ufcpp]

https://github.com/ufcpp/ContextFreeTask/pull/9