PEP-8
Implement assoc and update-in

Fixes #6.
PEP-8
Implement variadic comp

Generalizes the old PR, against the old functoolz, to provide any
arity to `comp`.
Add docstring and more tests for comp
Remove reference to Clojure in docstring of update_in
Clarify docstring for update_in
update update-in doctest
update assoc docstring

Also change variable names q/r to key/value

Simplify doctests to use more generic variable names
test immutability in assoc/update-in
add top-level imports for assoc/update_in
faster version of assoc

In [1]: from toolz import assoc

In [2]: data = dict(zip(range(10), range(10)))

In [3]: data
Out[3]: {0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}

In [4]: timeit assoc(data, 6, 6)
100000 loops, best of 3: 2.49 us per loop

In [5]: def assoc2(d, key, value):
   ...:     d2 = d.copy()
   ...:     d[key] = value
   ...:     return d
   ...:

In [6]: timeit assoc2(data, 6, 6)
1000000 loops, best of 3: 557 ns per loop
style changes in comp
change comp tests

remove groupby link

Add tests to cover multiple inputs and keyword arguments
Slightly clarify docstring for comp
Add two clarifying comments in tests
Merge pull request #10 from eigenhombre/multiple-arity-comp

Multiple arity comp
refine comp docstring
Merge pull request #9 from eigenhombre/add-assoc-update-in

Add assoc and update_in