make it possible to declare sections in the vimrc (#204).

t/airline.vim

@@ -1,4 +1,5 @@
 call airline#init#bootstrap()
+call airline#init#sections()
 
 function! MyFuncref(...)
   call a:1.add_raw('hello world')

t/commands.vim

@@ -1,4 +1,6 @@
 call airline#init#bootstrap()
+call airline#init#sections()
+
 source plugin/airline.vim
 
 describe 'commands'

t/extensions_default.vim

@@ -1,4 +1,5 @@
 call airline#init#bootstrap()
+call airline#init#sections()
 
 describe 'default'
   before

t/init.vim

@@ -10,6 +10,7 @@ describe 'init'
   before
     call s:clear()
     call airline#init#bootstrap()
+    call airline#init#sections()
   end
 
   after

t/section.vim

@@ -33,5 +33,10 @@ describe 'section'
     let s = airline#section#create(['hi'])
     Expect s == '%#hlgroup#hello'
   end
+
+  it 'should parse out a section from the vimrc'
+    let s = airline#section#create(['whitespace'])
+    Expect s =~ 'airline#extensions#whitespace#check'
+  end
 end