Make 'powerline' a namespace package

This will allow third-party plugins to use the 'powerline' namespace for
contributed segments.

Refs #3.
Fix “'NoneType' object is not iterable” error

Fixes #158
Revert "Make 'powerline' a namespace package"

This reverts commit 57bd0af2721bf5ad18b512f347d6a08468ce0767.
Add support for zsh/zpython

Closes #163.
Add solarized support for shell exit status segments

Closes #165.
Handle more request errors in common segments
Fix UTF-8 encoding issue with weather segment

Closes #172.
Fix repo.status() functions
Add repository_status vim segment

Split segment highlighting compared to the file_vcs_status segment is
missing.

Refs #173.
Fix e-mail segment UTF-8 issues

Closes #178.
Catch more errors in weather segment
Properly escape color codes in bash

Closes #177.
Closes #179.
Fix statusline highlighting after leaving a cmdwin

Because vim doesn't trigger any autocmds after leaving a cmdwin the
statusline in the window the user returned to from the cmdwin would be
highlighted as non-current even if it should have been current.

This issue is resolved by storing the last current window ID in a script
variable, and when leaving the cmdwin we show the last current window as
current instead of detecting it after the WinEnter autocmd has been
triggered (which doesn't happen after leaving a cmdwin).

Closes #184.
Improve vim plugin loading

Several of the plugin loading methods have been joined into one plugin
file that will be loaded by updating the runtimepath. More informative
error messages will be displayed if Python support is missing or if the
module import fails.

Note that this commit will break existing plugin loading, the new
method with updating the runtimepath will be required.

Closes #156.
Closes #181.
Add tips & tricks to the docs

Closes #182.
Fix math error in humanize_bytes

Closes #175.
Fix vim plugin path in Arch Linux packages
Add note about zpython branch

TODO: To be removed after (if) zsh maintainers accept the patch.

Refs #104.
Add modified_buffers segment

This segment returns a comma-separated list of modified buffers. The
segment is not enabled by default.

Closes #173.
Use functools.wraps on memoize decorator