Refactor arcTo method for improved calculations and error handling; add example test for arcTo functionality.

[CorleoneYu]

Fix arcTo implementation issues

Description

#101
This PR fixes several issues in the arcTo method implementation:

Changes

• Improved arcTo calculation logic: Refactored the arcTo method with better geometric calculations and error handling.
• Added new test case arcTo3.js to verify the fix
• Updated playground.html to include the new test case

Testing

Added a new test case test/example/arcTo3.js that demonstrates the fix:

window.C2S_EXAMPLES['arcTo3'] = function (ctx) {
    ctx.beginPath();
    ctx.moveTo(16,70);
    ctx.arcTo(16,74,20,74,4);
    ctx.stroke();
    ctx.closePath();
};

this case：
old

fixed

Related Issue

fixed

Fixes #101

Checklist

• Added test case as required by the project guidelines
• Code follows existing style and conventions
• All tests pass

[murkle]

This version isn't maintained any more. This is a newer maintained version: https://github.com/zenozeng/svgcanvas