Add configuration option and docs for 24-bit terminal colors

Closes #81.

docs/source/configuration.rst

@@ -52,6 +52,32 @@ Common configuration
 Common configuration is a subdictionary that is a value of ``common`` key in 
 :file:`powerline/config.json` file.
 
+``term_24bit_colors``
+    Defines whether to output a cterm index (8-bit) or RGB colors (24-bit) 
+    to the terminal emulator.
+
+    .. table:: 24-bit color support table
+       :name: term-rgb-color-support
+
+       ================== =====================
+       Terminal emulator  24-bit color support
+       ================== =====================
+       Gnome Terminal     |supp_no|
+       Gvim               |supp_no|
+       Konsole            |supp_yes|
+       lxterminal         |supp_no|
+       rxvt-unicode       |supp_no|
+       st                 |supp_no|
+       Xfce Terminal      |supp_no|
+       xterm              |supp_partial| [#]_
+       ================== =====================
+
+    .. |supp_yes| image:: _static/img/icons/tick.png
+    .. |supp_no| image:: _static/img/icons/cross.png
+    .. |supp_partial| image:: _static/img/icons/error.png
+
+    .. [#] Uses nearest color from 8-bit palette.
+
 ``dividers``
     Defines the dividers used in all Powerline extensions. This option 
     should usually only be changed if you don't have a patched font, or if 

powerline/config_files/config.json

@@ -1,5 +1,6 @@
 {
 	"common": {
+		"term_24bit_colors": false,
 		"dividers": {
 			"left": {
 				"hard": "",

powerline/core.py

@@ -46,7 +46,8 @@ class Powerline(object):
 		renderer_module_import = 'powerline.renderers.{0}'.format(renderer_module_name)
 		renderer_class_name = '{0}Renderer'.format(underscore_to_camelcase(renderer_module_name))
 		Renderer = getattr(importlib.import_module(renderer_module_import), renderer_class_name)
-		self.renderer = Renderer(theme_config, local_themes, theme_kwargs)
+		self.renderer = Renderer(theme_config, local_themes, theme_kwargs,
+			term_24bit_colors=self.config.get('term_24bit_colors', False))
 
 	def add_local_theme(self, key, config):
 		'''Add local themes at runtime (e.g. during vim session).

powerline/renderer.py

@@ -9,12 +9,13 @@ class Renderer(object):
 	ATTR_ITALIC = 2
 	ATTR_UNDERLINE = 4
 
-	TERM_24BIT = False
+	TERM_24BIT_COLORS = False
 
-	def __init__(self, theme_config, local_themes, theme_kwargs):
+	def __init__(self, theme_config, local_themes, theme_kwargs, term_24bit_colors=False):
 		self.theme = Theme(theme_config=theme_config, **theme_kwargs)
 		self.local_themes = local_themes
 		self.theme_kwargs = theme_kwargs
+		self.TERM_24BIT_COLORS = term_24bit_colors
 
 	def add_local_theme(self, matcher, theme):
 		if matcher in self.local_themes:

powerline/renderers/shell.py

@@ -17,7 +17,7 @@ class ShellRenderer(Renderer):
 			if fg is False or fg[0] is False:
 				ansi += [39]
 			else:
-				if self.TERM_24BIT:
+				if self.TERM_24BIT_COLORS:
 					ansi += [38, 2] + list(self._int_to_rgb(fg[1]))
 				else:
 					ansi += [38, 5, fg[0]]
@@ -25,7 +25,7 @@ class ShellRenderer(Renderer):
 			if bg is False or bg[0] is False:
 				ansi += [49]
 			else:
-				if self.TERM_24BIT:
+				if self.TERM_24BIT_COLORS:
 					ansi += [48, 2] + list(self._int_to_rgb(bg[1]))
 				else:
 					ansi += [48, 5, bg[0]]