Add terminal_colors for neovim

Neovim has support for embedded terminals. However, the colors do not inherit
from the parent shell settings, and end up looking funky. This commit adds 16
color support for Neovim's terminal.

See: https://github.com/neovim/neovim/issues/2897#issuecomment-115464516

colors/gruvbox.vim

@@ -131,6 +131,43 @@ let s:gb.faded_purple   = ['#8f3f71', 96]      " 143-63-113
 let s:gb.faded_aqua     = ['#427b58', 66]      " 66-123-88
 let s:gb.faded_orange   = ['#af3a03', 130]     " 175-58-3
 
+" }}}
+" Setup Terminal Colors For Neovim: {{{
+
+if has('nvim')
+  " dark0 + gray
+  let g:terminal_color_0 = "#282828"
+  let g:terminal_color_8 = "#928374"
+
+  " neurtral_red + bright_red
+  let g:terminal_color_1 = "#cc241d"
+  let g:terminal_color_9 = "#fb4934"
+
+  " neutral_green + bright_green
+  let g:terminal_color_2 = "#98971a"
+  let g:terminal_color_10 = "#b8bb26"
+
+  " neutral_yellow + bright_yellow
+  let g:terminal_color_3 = "#d79921"
+  let g:terminal_color_11 = "#fabd2f"
+
+  " neutral_blue + bright_blue
+  let g:terminal_color_4 = "#458588"
+  let g:terminal_color_12 = "#83a598"
+
+  " neutral_purple + bright_purple
+  let g:terminal_color_5 = "#b16286"
+  let g:terminal_color_13 = "#d3869b"
+
+  " neutral_aqua + faded_aqua
+  let g:terminal_color_6 = "#689d6a"
+  let g:terminal_color_14 = "#8ec07c"
+
+  " light4 + light1
+  let g:terminal_color_7 = "#a89984"
+  let g:terminal_color_15 = "#ebdbb2"
+endif
+
 " }}}
 " Setup Emphasis: {{{