Fix whitespace issues so pyflakes doesn't complain
Improve unicode handling of rendered segments
Handle remainder whitespace for filler segments

When more than one filler segment is specified it may sometimes be
a remainder when calculating the amount of whitespace. divmod() is used
to retrieve the remainder, which is added as whitespace to the first
filler segment.
Fix issues with the terminal prompt example
Make vim example work with split and inactive windows

This commit introduces a bunch of changes. Most importantly, it ensures
that split windows and inactive windows work as expected. This is
accomplished with some clever workarounds for vim's statusline
limitations.

Vim statuslines evaluated using the %! statusline item are always
evaluated in the buffer context and not in the statusline's owner
window's context, and this made the previous implementation show the
same statusline for all windows. The only way to ensure that the correct
statusline is rendered to the correct window is to walk through all
windows, and setting the statuslines with a reference to the current
window number every time the current window is changed. This is
accomplished by a set of BufEnter, BufLeave, etc. autocommands.

The Syntastic segment has been temporarily removed due to errors when
referencing the statusline function before Syntastic has been loaded.
Improve rendering performance

This commit almost doubles the segment rendering performance. This is
accomplished by caching a lot of data like highlighting groups, moving
some calculations out of loops, and by performing less function calls
overall.

When a width is specified the main speed improvement comes from avoiding
rendering the raw segments over and over until the statusline is short
enough. Instead, the raw rendering is stored as a segment property and
the combined length of all these renderings is used when removing
low-priority segments instead. This results in a maximum of two
rendering passes.

Some "less pythonic" solutions have been chosen some places for
performance reasons, e.g. joining strings instead of appending and
joining lists.

Overall this commit appears to make the performance equal or better than
the legacy vimscript implementation. Later optimizations (in particular
finding another method than remove() for removing low-priority segments)
may make this version of Powerline far superior both in terms of
functionality and performance.
Improve rendering performance

This change removes the Segment class as this takes forever to remove
from the segment array when removing low-priority segments. It has
instead been replaced by a wrapper function that works the same and
returns a working dict of all segment properties.

The regex substitution bottleneck in the vim example has been fixed by
using a single-character percent placeholder in vim segments which is
later replaced with a double percent using str.replace().
Fix various rendering issues

Another rendering pass is necessary before calculating the filler
segment's lengths, because center segments may lose their separators
after removing low-priority segments.

Some unicode and variable assignment issues has been resolved so
everything renders correctly.
Merge branch 'feature/extended-vim-example' into develop