added page_indicator to show document position and rendering

idea is simple: when starting long operation (page renedering) invert
box on top of screen which has relative width of this page.

This allows easy overview where in document user is, along with
indication that something is still happending.

Perfect use-case are glossy magazines pdfs which have first two
pages in hi-res graphics, so this indicator is very useful to see
that something is still happending and that reader didn't die

unireader.lua

@@ -1046,6 +1046,14 @@ function UniReader:drawOrCache(no, preCache)
 	-- #3 goal: we render the full page
 	-- #4 goal: we render next page, too. (TODO)
 
+	local pg_w = G_width / ( self.doc:getPages() )
+	local page_indicator = function() 
+		fb.bb:invertRect( pg_w*(no-1),0, pg_w,10)
+		fb:refresh(1,     pg_w*(no-1),0, pg_w,10)
+		Debug('page_indicator',no)
+	end
+	page_indicator()
+
 	-- ideally, this should be factored out and only be called when needed (TODO)
 	local ok, page = pcall(self.doc.openPage, self.doc, no)
 	local width, height = G_width, G_height
@@ -1083,6 +1091,9 @@ function UniReader:drawOrCache(no, preCache)
 				self.cache[pagehash].ttl = self.cache_max_ttl
 			end
 			-- ...and return blitbuffer plus offset into it
+
+			page_indicator()
+
 			return pagehash,
 				offset_x_in_page - self.cache[pagehash].x,
 				offset_y_in_page - self.cache[pagehash].y
@@ -1145,6 +1156,8 @@ function UniReader:drawOrCache(no, preCache)
 	page:draw(dc, self.cache[pagehash].bb, 0, 0, self.render_mode)
 	page:close()
 
+	page_indicator()
+
 	-- return hash and offset within blitbuffer
 	return pagehash,
 		offset_x_in_page - tile.x,