move highlighter code to correct place and test.

t/highligher.vim

@@ -0,0 +1,10 @@
+describe 'highlighter'
+  it 'should create separator highlight groups'
+    hi Foo1 ctermfg=1 ctermbg=2
+    hi Foo2 ctermfg=3 ctermbg=4
+    call airline#highlighter#add_separator('Foo1', 'Foo2', 0)
+    let hl = airline#highlighter#get_highlight('Foo1_to_Foo2')
+    Expect hl == [ '', '', '4', '2', '' ]
+  end
+end
+

t/themes.vim

@@ -25,5 +25,13 @@ describe 'themes'
     Expect colors[2] == '222'
     Expect colors[3] == '103'
   end
+
+  it 'should pass args through correctly'
+    let hl = airline#themes#get_highlight('Foo', 'bold', 'italic')
+    Expect hl == ['', '', 0, 1, 'bold,italic']
+
+    let hl = airline#themes#get_highlight2(['Foo','bg'], ['Foo','fg'], 'italic', 'bold')
+    Expect hl == ['', '', 1, 0, 'italic,bold']
+  end
 end