fix: scale-direction for element when it rotated

• refactor: refactor idraw.exportDataURL
• feat: @idraw/core add free render status
• feat: Add event drawFrame and drawFrameComplete
• feat: @idraw/core add method setOnlyRender and cancelOnlyRender

• fix: fix the scaling state should be adjusted when rotating elements

• feat: Add method getElement and getElementByIndex
• fix: It can listen doubleClickElement when the element is invisible

• feat: add keyboard event for undo
• refactor: refactor @idraw/core lib/*
• refactor: @idraw/core mix element methods
• chore: update text element desc prop
• chore: add demo base on react and vue

• refactor: rename desc.color tp desc.bgColor for rect and circle
• feat: add returns to insertElement methods

• feat: add getSelectedElements to @idraw/core
• feat: add keyboard event to copy/cut/paste elements
• feat: add keyboard event to controll scroll

• feat: add clearOperation and operation attribute
• refactor: resource reload logic
• fix: resource loader logic

• feat: add clearOperation method to idraw for clear all select status #69
• refactor: add attr operation: {[key: string]: any} to Element and replace lock #69
• refactor: add attr extension: {[key: string]: any} to Element #69

• feat: @idraw/board add doubleClick event
• feat: add event named screenDoubleClickElement to @idraw/core
• fix: exportDataURL can't export image completely when idraw scale canvas