Mouse-drawing on canvas

[acrm]

Before we use more sophisticated tools for web-pages design, let's create more interesting business-logic. Our current goal - site, on which we could draw some sketches by mouse and save this sketches for users.

Tasks:

• [x] When mouse moving with pressed left button it leaves a track of lines on the canvas
• [x] Keep sequence of points, that were generated while drawing. Add 'Save' button, when it clicked, output list of points in JS console
• [ ] Invent some heuristics to reduce number of used point with saving general shape of drawings.

[acrm]

For saving our drawings we should transport clicks collection to server and store them in some fie.

• [x] Add to Save button click handler code that serialize clicks collection to JSON and send it via XmlHttpRequest object to /canvas/save url by POST method. Don't forget ContentType header.
• [x] In the server middleware add code that catch /canvas/save request, check that they have POST method, read request body json and save in the folder data in separate file with current timestamp as name with json extension
• [x] Add code to the Canvas page, that read the last json file from data folder, and put it content in savedData variable in page's javascript. Update javascript code such way, that in initialization it check savedData variable and draw clicks from it.