feat: redesign background shades

Change the background to a darker variant of the original, I then
created shades by mixing in white to create alternative xgray[n]
variants.

The new background was chosen so that the colors pop a bit more, trying
out srcery on various monitors of often looked washed out. I've also
gotten my hands on a much better monitor, so I'm more able to accurately
cover multiple various outputs.

Author: roosta

colors/srcery.vim

@@ -22,7 +22,7 @@ let g:colors_name='srcery'
 " Colors
 " ---------
 if !exists('g:srcery_black')
-  let g:srcery_black='#1C1B19'
+  let g:srcery_black='#121110'
 endif
 
 if !exists('g:srcery_red')
@@ -50,11 +50,11 @@ if !exists('g:srcery_cyan')
 endif
 
 if !exists('g:srcery_white')
-  let g:srcery_white='#BAA67F'
+  let g:srcery_white='#C5B088'
 endif
 
 if !exists('g:srcery_bright_black')
-  let g:srcery_bright_black='#918175'
+  let g:srcery_bright_black='#917E6B'
 endif
 
 if !exists('g:srcery_bright_red')
@@ -110,47 +110,47 @@ if !exists('g:srcery_hard_black_cterm')
 endif
 
 if !exists('g:srcery_xgray1')
-  let g:srcery_xgray1='#262626'
+  let g:srcery_xgray1='#1c1b19'
 endif
 
 if !exists('g:srcery_xgray1_cterm')
   let g:srcery_xgray1_cterm=235
 endif
 
 if !exists('g:srcery_xgray2')
-  let g:srcery_xgray2='#303030'
+  let g:srcery_xgray2='#262522'
 endif
 
 if !exists('g:srcery_xgray2_cterm')
   let g:srcery_xgray2_cterm=236
 endif
 
 if !exists('g:srcery_xgray3')
-  let g:srcery_xgray3='#3A3A3A'
+  let g:srcery_xgray3='#312f2c'
 endif
 
 if !exists('g:srcery_xgray3_cterm')
   let g:srcery_xgray3_cterm=237
 endif
 
 if !exists('g:srcery_xgray4')
-  let g:srcery_xgray4='#444444'
+  let g:srcery_xgray4='#3b3935'
 endif
 
 if !exists('g:srcery_xgray4_cterm')
   let g:srcery_xgray4_cterm=238
 endif
 
 if !exists('g:srcery_xgray5')
-  let g:srcery_xgray5='#4E4E4E'
+  let g:srcery_xgray5='#45433e'
 endif
 
 if !exists('g:srcery_xgray5_cterm')
   let g:srcery_xgray5_cterm=239
 endif
 
 if !exists('g:srcery_xgray6')
-  let g:srcery_xgray6='#585858'
+  let g:srcery_xgray6='#504d47'
 endif
 
 if !exists('g:srcery_xgray6_cterm')