py: Replace py-version.sh with makeversionhdr.py, written in Python.

Also rename py-version.h to mpversion.h for consistency with mpconfig.h.
diff --git a/py/makeversionhdr.py b/py/makeversionhdr.py
new file mode 100644
index 0000000..e37496d
--- /dev/null
+++ b/py/makeversionhdr.py
@@ -0,0 +1,64 @@
+# This script works with Python 2 and 3
+
+from __future__ import print_function
+
+import sys
+import os
+import datetime
+import subprocess
+
+def make_version_header(filename):
+    # Note: git describe doesn't work if no tag is available
+    try:
+        git_tag = subprocess.check_output(["git", "describe", "--dirty", "--always"], universal_newlines=True).strip()
+    except subprocess.CalledProcessError:
+        git_tag = ""
+    try:
+        git_hash = subprocess.check_output(["git", "rev-parse", "--short", "HEAD"], stderr=subprocess.STDOUT, universal_newlines=True).strip()
+    except subprocess.CalledProcessError:
+        git_hash = "unknown"
+
+    try:
+        # Check if there are any modified files.
+        subprocess.check_call(["git", "diff", "--no-ext-diff", "--quiet", "--exit-code"], stderr=subprocess.STDOUT)
+        # Check if there are any staged files.
+        subprocess.check_call(["git", "diff-index", "--cached", "--quiet", "HEAD", "--"], stderr=subprocess.STDOUT)
+    except subprocess.CalledProcessError:
+        git_hash += "-dirty"
+
+    # Try to extract MicroPython version from git tag
+    if git_tag.startswith("v"):
+        ver = git_tag[1:].split("-")[0].split(".")
+        if len(ver) == 2:
+            ver.append("0")
+    else:
+        ver = ["0", "0", "1"]
+
+    # Generate the file with the git and version info
+    file_data = """\
+// This file was generated by py/makeversionhdr.py
+#define MICROPY_GIT_TAG "%s"
+#define MICROPY_GIT_HASH "%s"
+#define MICROPY_BUILD_DATE "%s"
+#define MICROPY_VERSION_MAJOR (%s)
+#define MICROPY_VERSION_MINOR (%s)
+#define MICROPY_VERSION_MICRO (%s)
+#define MICROPY_VERSION_STRING "%s.%s.%s"
+""" % (git_tag, git_hash, datetime.date.today().strftime("%Y-%m-%d"),
+    ver[0], ver[1], ver[2], ver[0], ver[1], ver[2])
+
+    # Check if the file contents changed from last time
+    write_file = True
+    if os.path.isfile(filename):
+        with open(filename, 'r') as f:
+            existing_data = f.read()
+        if existing_data == file_data:
+            write_file = False
+
+    # Only write the file if we need to
+    if write_file:
+        print("Generating %s" % filename)
+        with open(filename, 'w') as f:
+            f.write(file_data)
+
+make_version_header(sys.argv[1])