Add options to tweak spacegray

Adds italic comment support and the ability to use underline instead of
the highlight search, which makes it much more pleasing to look at, in
my opinion.

Note that the italic comment support in terminal vim requires terminal
support.

README.md

@@ -3,6 +3,20 @@
 Spacegray is a colorscheme for Vim loosely modeled after
 the [spacegray](https://github.com/zdne/spacegray-xcode) theme for Xcode.
 
+## Options
+
+You can tweak Spacegray by enabling the following disabled options:
+
+1. Underlined Search: Underline search text instead of using highlight color.
+   Put the following in your `~/.vimrc` to enable it:
+
+  > `let g:spacegray_underline_search = 1`
+
+2. Italic Comments: Italicize comments (_note_: vim requires terminal support).
+   Put the following in your `~/.vimrc` to enable it:
+
+  > `let g:spacegray_italicize_comments = 1`
+
 ## Screenshots
 
 Here are a few screenshots of Spacegray:

colors/spacegray.vim

@@ -11,6 +11,14 @@ if exists('syntax_on')
   syntax reset
 endif
 
+if !exists('g:spacegray_underline_search')
+  let g:spacegray_underline_search = 0
+endif
+
+if !exists('g:spacegray_italicize_comments')
+  let g:spacegray_italicize_comments = 0
+endif
+
 set background=dark
 let colors_name = 'spacegray'
 
@@ -18,7 +26,11 @@ let colors_name = 'spacegray'
 hi Normal          ctermbg=233  ctermfg=250    guibg=#111314  guifg=#B3B8C4  cterm=NONE      gui=NONE
 hi Conceal         ctermbg=NONE ctermfg=250    guibg=NONE     guifg=#B3B8C4  cterm=NONE      gui=NONE
 
-hi Comment         ctermbg=NONE ctermfg=59     guibg=NONE     guifg=#515F6A  cterm=NONE      gui=NONE
+if g:spacegray_italicize_comments
+  hi Comment       ctermbg=NONE ctermfg=59     guibg=NONE     guifg=#515F6A  cterm=italic    gui=italic
+else
+  hi Comment       ctermbg=NONE ctermfg=59     guibg=NONE     guifg=#515F6A  cterm=NONE      gui=NONE
+endif
 hi NonText         ctermbg=NONE ctermfg=8      guibg=NONE     guifg=#3E4853  cterm=NONE      gui=NONE
 hi Title           ctermbg=NONE ctermfg=231    guibg=NONE     guifg=#FFFFFF  cterm=NONE      gui=NONE
 
@@ -78,7 +90,11 @@ hi Folded          ctermbg=NONE ctermfg=242    guibg=#1C1C1C  guifg=#6C6C6C  cte
 hi VertSplit       ctermbg=238  ctermfg=238    guibg=#444444  guifg=#444444  cterm=NONE      gui=NONE
 
 hi IncSearch       ctermbg=9    ctermfg=0      guibg=#AF5F5F  guifg=#141617  cterm=NONE      gui=NONE
-hi Search          ctermbg=2    ctermfg=232    guibg=#919652  guifg=#141617  cterm=NONE      gui=NONE
+if g:spacegray_underline_search
+  hi Search        ctermbg=NONE ctermfg=NONE   guibg=NONE     guifg=NONE     cterm=underline gui=underline
+else
+  hi Search        ctermbg=2    ctermfg=232    guibg=#919652  guifg=#141617  cterm=NONE      gui=NONE
+endif
 
 hi TabLine         ctermbg=232  ctermfg=249    guibg=#141617  guifg=#B3B8C4  cterm=NONE      gui=NONE
 hi TabLineFill     ctermbg=235  ctermfg=239    guibg=#303537  guifg=#303537  cterm=NONE      gui=NONE