Refactor switching to process buffer

For easier testability
Implement process view buffer truncation
Switch to hook-based truncate implementation

Makes process output more user-customizable.
Rename :truncate property to :truncate-output
Use hooks to deal with process output
Refactor handling of output from processes.
Rename function.
Require ert-async to avoid compiler warnings.
Add support for truncate output tag inheritance.
Merge branch 'truncate-views' into v0.4-wip

Conflicts:
	prodigy.el
Get rid of some compiler warnings.
Must inject service.

Not sure why this worked before?
Fix service env accessor uniq bug.