existing tests pass with threshold as a function

implements #6
test for threshold function (in|ex)cluding files from common (for #6)
Unsuccessful attempt to ensure dependees end up in common with their dependents.

self._buffered would need to topologically sorted for this to work
proof of concept: topo sort module-deps output
0.0.2
reenable deep compare in complicated deps test
document opts.threshold(row)
80 cols
0.1.0
each test file gets its own test dir
passing lift test