Fix long_description string in Python packaging (pinterest#249)

When defining `long_description` in setup.cfg using the `file:`
directive, we need to keep everything on one line. Otherwise, it will
treat the value as a block of literal text.

Fix flags when setting multiple values at once (pinterest#248)

We introduced the ability to override the serializer-returned flags
values in 26f7c1b. Unfortunately, there was a flaw in that logic which
resulted in the first item's flags being used for all later items. This
bug primarily affected set_many()'s behavior when the data dictionary
contained multiple different value types which were assigned different
per-value flags values by the serializer.

For example:

    set_many({'a': 'string', 'b': 10})

If a serializer returned different flags for strings (e.g. 1) and
integer values (e.g. 2), the previous logic would have set ``flags``
to 1 the first time through the loop and repeated that value for the
second item, instead of using 2.

This was the intended behavior when ``flags`` was explicitly passed to
set_many(), but not for the default case where we still want to respect
the flags values returned by the serializer.

Bump documentation version for 2.2.0 release

Merge pull request pinterest#216 from jparise/setup-version

Parse version directly from pymemcache/__init__.py

Merge pull request pinterest#212 from jparise/prepare-2.1.0

Finish preparing the 2.1.0 release

Merge pull request pinterest#189 from jogo/2.0

Prepare for release of 2.0.0

Update changelog

Changelog changes for 1.4.3

Changelog for 1.4.2

Add changelog for 1.4.1