add simple tests and timing code

The tests here may not be much use to you, but typing them out was useful to me in examining the library's workings. There are two files, meant for use with `pytest`:

 * `test_docs_content.py` reproduces most of the tests in the docstrings.
 * `test_large_lists.py` creates some large lists and tests `inverse` and `get_item` on their instantiations as `bidict`s.

The little timing program shows me how much slower `bidict` is than just creating a reversed dictionary. Of course, creation happens only once, and after that there are considerable savings in space and functionality. I am not suggesting any changes to `bidict` on account of this — I just wanted to see the difference in timing.

```python
>>> import time_manual_reverse_dict as M
>>> M.main(200)
Example with int: str.
In 200 trials, average time for a list of cardinality 100000:
    bidict:        1.8498 sec.
    reversed dict: 0.0349 sec.

Example with str: int.
In 200 trials, average time for a list of cardinality 100000:
    bidict:        1.8675 sec.
    reversed dict: 0.0378 sec.
>>>
```
Actually, I meant the range [lo, hi]. Thanks for these helpful corrections,
more careful than my own work.

- dpb


On Sat, Sep 27, 2014 at 10:20 AM, jab <notifications@github.com> wrote:

> In test/test_large_lists.py:
>
> > @@ -0,0 +1,57 @@
> > +# test_large_lists.py
> > +# David Prager Branner
> > +# 20140925
> > +
> > +"""Supply tests with large lists of randomly constructed items."""
> > +
> > +import bidict as B
> > +import pytest
> > +import random
> > +import string
> > +
> > +def random_ints(cardinality=10, hi=10, lo=-10):
> > +    """return list of `cardinality` ints, each in range (lo, hi)."""
>
> In common math notation a parenthesis in an interval means non-inclusive,
> so using (lo, hi) here (with a space after range) could be confused to
> mean lo + 1, lo + 2, ..., hi - 1. Could remove the space and add
> backticks around range to make it clearer your comparing with a call to
> Python's range rather than just using the mathematical term. Or better
> yet, explicitly say "from lo to hi - 1".
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/jab/bidict/pull/1/files#r18123837>.
>