Bumps version to 0.28a1.

[ci skip]
Adds new WIP iostream module.

[ci skip]
connection.py: Fixes unbound variables.
web.py: Catch and rethrows bad redirect URL errors.

Closes chfoo/wpull#87
iostream.py: Adds WIP DataBuffer and IOStream methods.

[ci skip]
iostream.py: Adds WIP SSLIOStream.

[ci skip]
connection.py: Swaps in WIP iostream.

[ci skip]
iostream.py: WIP adds read/write fast path & exception handling.
badapp.py: Fixes TCP reset unit test.
iostream: Logs spurious events as debug.
iostream.py: Friendlier events error messages.
connection.py: Closes connection if HTTP Connection is close.
iostream.py: Adds functions to monitor for socket close.
connection.py: Monitors for stream close.
connection.py: Implements proper keep-alive check. Skips impossible unit test.
iostream.py: Loops recv to account for SSL.
writer.py: Fixes root not used in PathNamer.
Adds payload equality unit test.
changelog: Adds entry about new iostream.

extended.py: Adds deprecation notice.

Closes chfoo/wpull#53
Merge branch 'topic/iostream_rewrite' into develop

Conflicts:
	doc/changelog.rst