Added REPL support

Closes #9
Closes #12

autoload/features/repl.vim

@@ -0,0 +1,67 @@
+if exists("s:loaded")
+    finish
+endif
+let s:loaded = 1
+
+let s:repl_pid = -1
+let s:repl_window = -1
+
+function! s:Window()
+    return winbufnr(s:repl_window)
+endfunction
+
+function! s:IsOpen()
+    return winbufnr(s:Window()) > 0
+endfunction
+
+function! s:Focus()
+    if s:IsOpen()
+        exec ":" . s:Window() . "wincmd w"
+    endif
+endfunction
+
+function! features#repl#start()
+    if s:IsOpen()
+        call s:Focus()
+    else
+        if g:nvim_nim_repl_vsplit
+            vnew
+            wincmd L
+            wincmd L
+            wincmd L
+        else
+            new
+            wincmd J
+            wincmd J
+            wincmd J
+        endif
+
+        let s:repl_window = winnr()
+        let s:repl_pid = termopen("sh -c \"nim secret\"")
+    endif
+endfunction
+
+function! features#repl#send(lines)
+    if !s:IsOpen()
+        call features#repl#start()
+        sleep 100m
+    endif
+
+    for line in a:lines
+        call jobsend(s:repl_pid, line . "\r")
+        sleep 20m
+    endfor
+    call jobsend(s:repl_pid, "\r")
+    sleep 20m
+    norm! i
+endfunction
+
+function! features#repl#stop()
+    if s:repl_pid > 0
+        call jobstop(s:repl_pid)
+        call s:Focus()
+        exec ":bd!"
+    else
+        echom "No REPL running"
+    endif
+endfunction