Stop building a JAR file.

It's no longer necessary to build a JAR file in the newer versions of
Thunderbird we're targeting, and it doesn't really provide any benefits.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Reindent Makefile.

The mix of tabs and spaces is bizarre and makes it hard to tell that it's
actually all one command.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Update README.

Explicitly spell out the license and contribution information.  Expand the
description somewhat.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Reindent files to use tabs.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Fix grammar error and typo.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Improve temporary file generation.

The previous temporary file generation algorithm was based on the time, which is
completely predictable; this is a security issue.  Improve this by generating a
128-bit random value and using that, hex-encoded, as the temporary file name.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>