Add initial function for counting commits over time periods

This just starts at the beginning of 2014 and cranks through

bin/commit-counter

@@ -0,0 +1,41 @@
+#!/usr/bin/env python
+import argparse
+import datetime
+import jinja2
+import os
+import subprocess
+import teamanalysis.git
+import teamanalysis.repos
+import teamanalysis.time
+import webbrowser
+
+def _get_commits(repo, start, end):
+    abspath = '/Users/eliribble/src/{}/'.format(repo)
+    os.chdir(abspath)
+    command = [
+            'git',
+            'log',
+            '--pretty=format:"%h %aI"',
+            '--after={}'.format(start.isoformat()),
+            '--before={}'.format(end.isoformat())]
+    output = subprocess.check_output(command)
+    return output
+
+def _show_summary(timepoint):
+    start, end = teamanalysis.time.get_checkpoint(timepoint)
+    results = {}
+    for repo in teamanalysis.repos.REPOSITORIES:
+        output = _get_commits(repo, start, end)
+        lines = output.split('\n')
+        results[repo] = len(lines) if output else 0
+        #print("{0:<30}: {1}".format(repo, results[repo]))
+    print("{}\t{}\t{}".format(start.date().isoformat(), end.date().isoformat(), sum(results.values())))
+
+def main():
+    timepoint = datetime.datetime(2014, 1, 1, 0, 0, 1)
+    while timepoint < datetime.datetime.utcnow():
+        _show_summary(timepoint)
+        timepoint = timepoint + datetime.timedelta(days=7)
+
+if __name__ == '__main__':
+    main()