Update README with more obvious link to docs

Hello :)
Support python3.3!

Relatively painless.
Update benchmark script to be py3.3 compatible
Use bytes for keys and values (and implicitly convert str)

bytes/bytearray should be used for keys and values.  However,
one not-so-great decision for the dbm interface in python3.x is
that keys and values are implicitly converted to bytes for you.
IMO I'd either require strs for everything and internally use
utf-8, *or* require that bytes *must* be used for key/values,
and error out if that's not the case.  The way it is now, you
have confusing semantics where::

    val = 'bar'
    db['foo'] =  val
    assert db['foo'] == val # This will fail.

You also can now access a key be either a str or bytes value:

    db['foo'] =  'bar'
    db['foo'] # returns b'bar'
    db[b'foo']# returns b'bar'

However, if we want to be able to be a drop in replacement
for other python dbms (which we do) we have to support this
weird and non-intuitive API design choice.  Damn.
Print full traceback on benchmark errors
Fix int() bug in benchmark script
Add travis.yml config
Fix unittest2 issue for py26

Also removed the coveralls stuff because
the reporting tool doesn't support python3.3
Add travis.ci img to README
Fix typo
Fix encoding but with python2.x

In python2.x we only encode to utf-8 if
we're giving a unicode type.  For a str type,
we assume it's a byte string.
Bind _str_type to locals in get/set/delitem
Fix api_semidbm import names
Add fileformat spec
Switch db file to binary format
Add header info to binary file format

Only verifying major versions.  Minor versions
should be compatible.
Remove irrelevant test helper method
Merge branch 'binary-format'

This branch contains the work to switch from
a pure ASCII format to a binary format.  This brings
performance increases and simplified logic for loading
a db file.

I've also added version info to the file format, to help
determine if this a file we can load.

This new format is documented in the sphinx docs.

* binary-format:
  Remove irrelevant test helper method
  Add header info to binary file format
  Switch db file to binary format
  Add fileformat spec
  Fix api_semidbm import names
Use bytes instead of str for benchmarks

So bsddb3 actually just requires bytes for key/values
so this is needed if we want to benchmark bsddb3.  Though
if I could remove the isinstance checks in semidbm, I'd get
a small performance boost as well ;)

The benchmarks for bsddb3 and semidbm are fairly close for
1000000 keys, though for smaller key sizes bsddb3 is much
faster than semidbm.
Update docs and changelog with latest changes