Save auto-generated font metrics data to separate JSON file

This separates auto-generated code from manually created code.
We need a more recent version of browserify to directly require JSON.
Note that the data was copied, not recreated, so it has not been changed.
This addresses issue #301.

metrics/README.md

@@ -17,5 +17,5 @@ Once you have these things, run
 
     make metrics
 
-which should generate new metrics and place them into `fontMetrics.js`. You're
-done!
+which should generate new metrics and place them into `fontMetricsData.json`.
+You're done!

metrics/replace_line.py

@@ -1,17 +0,0 @@
-#!/usr/bin/env python2
-
-import sys
-
-with open("../src/fontMetrics.js", "r") as metrics:
-    old_lines = file.readlines(metrics)
-
-replace = sys.stdin.read()
-
-with open("../src/fontMetrics.js", "w") as output:
-    for line in old_lines:
-        if line.startswith("var metricMap"):
-            output.write("var metricMap = ")
-            output.write(replace)
-            output.write(";\n")
-        else:
-            output.write(line)