Add line_width parameter

Author: martinRenou

examples/lines.ipynb

@@ -0,0 +1,71 @@
+{
+ "cells": [
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "from ipycanvas import Canvas"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Line width"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "size = (200, 140)\n",
+    "\n",
+    "canvas = Canvas(size=size)\n",
+    "for i in range(10):\n",
+    "    width = 1 + i\n",
+    "    x = 5 + i * 20\n",
+    "    canvas.line_width = width\n",
+    "\n",
+    "    canvas.fill_text(str(width), x - 5, 15)\n",
+    "\n",
+    "    canvas.begin_path()\n",
+    "    canvas.move_to(x, 20)\n",
+    "    canvas.line_to(x, 140)\n",
+    "    canvas.stroke()\n",
+    "canvas"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": []
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.7.3"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 4
+}

ipycanvas/canvas.py

@@ -74,6 +74,9 @@ class Canvas(DOMWidget):
         default_value='source-over'
     )
 
+    #: (float) Sets the width of lines drawn in the future, must be a positive number. Default to ``1.0``.
+    line_width = Float(1.0)
+
     def __init__(self, *args, **kwargs):
         """Create a Canvas widget."""
         #: Whether commands should be cached or not
@@ -268,7 +271,8 @@ def flush(self):
         self._buffers_cache = []
 
     @observe('fill_style', 'stroke_style', 'global_alpha', 'font', 'text_align',
-             'text_baseline', 'direction', 'global_composite_operation')
+             'text_baseline', 'direction', 'global_composite_operation',
+             'line_width')
     def _on_set_attr(self, change):
         command = {
             'name': 'set',