Create dynamic vim statusline example

This example only does a single type of highlighting (normal mode) but
demonstrates nicely how rendering a statusline with Python could work.
This also utilizes the new width functionality to crop away less
important segment if the window is too small, and do the padding with
Python instead of using vim's split segment.

Some optimization will probably be necessary, as calling Python for each
statusline redraw is quite expensive. A solution could be evaluating the
segments in Python once and then calculating the width and crop away/pad
the segments, and then sending the statusline with unevaluated segments
to vim for rendering without calling Python. Only some events (like
CursorHold, InsertEnter/InsertLeave, etc.) would trigger a re-render
with Python, a recalculation of the width and cropping/padding.

powerline-vim-example.vim

@@ -0,0 +1,55 @@
+" Powerline vim example
+" Run with :source %
+
+let s:did_highlighting = 0
+let s:segments = [
+	\ { 'contents': 'mode()',                  'fg': 22,  'bg': 148, 'attr': 1 },
+	\ { 'contents': '"⭠ develop"',             'fg': 247, 'bg': 240, 'priority': 10 },
+	\ { 'contents': '" ".expand("%:p:h")."/"', 'fg': 250, 'bg': 240, 'padding': '', 'draw_divider': 0, 'priority': 5 },
+	\ { 'contents': 'expand("%:p:t")." "',     'fg': 231, 'bg': 240, 'padding': '', 'attr': 1 },
+	\ { 'filler': 1 },
+	\ { 'contents': '&ff',                     'fg': 245, 'bg': 236, 'side': 'r', 'priority': 50 },
+	\ { 'contents': '&fenc',                   'fg': 245, 'bg': 236, 'side': 'r', 'priority': 50 },
+	\ { 'contents': '&ft',                     'fg': 245, 'bg': 236, 'side': 'r', 'priority': 50 },
+	\ { 'contents': '(line(".") * 100 / line("$") * 100) / 100 . "%%"', 'fg': 247, 'bg': 240, 'side': 'r', 'priority': 30 },
+	\ { 'contents': '"⭡"',                     'fg': 239, 'bg': 252, 'side': 'r' },
+	\ { 'contents': 'line(".")',               'fg': 239, 'bg': 252, 'side': 'r', 'attr': 1, 'padding': '', 'draw_divider': 0 },
+	\ { 'contents': '":". col(".")',           'fg': 244, 'bg': 252, 'side': 'r', 'padding': '', 'draw_divider': 0, 'priority': 30 },
+\ ]
+
+function! DynStl()
+	python <<EOF
+import vim
+import sys
+sys.path.append('.')
+
+from lib.core import Segment
+from lib.renderers import VimSegmentRenderer
+
+winwidth = int(vim.eval('winwidth(0)'))
+segments = [{
+		'contents': vim.eval(s.get('contents', '""')),
+		'fg': int(s.get('fg', 0)) or None,
+		'bg': int(s.get('bg', 0)) or None,
+		'attr': int(s.get('attr', 0)),
+		'priority': int(s.get('priority', -1)),
+		'padding': s.get('padding', ' '),
+		'draw_divider': int(s.get('draw_divider', 1)),
+		'filler': bool(s.get('filler', 0)),
+		'side': s.get('side', 'l'),
+	} for s in vim.eval('s:segments')]
+
+powerline = Segment([Segment(**segment) for segment in segments], 236, 236)
+
+renderer = VimSegmentRenderer()
+stl = powerline.render(renderer, winwidth)
+
+if int(vim.eval('s:did_highlighting')) == 0:
+	vim.command(renderer.get_hl_statements())
+	vim.command('let s:did_highlighting = 1')
+
+vim.command('return "{0}"'.format(stl))
+EOF
+endfunction
+
+let &stl = '%!DynStl()'