Update the clang-redist paths in the README.
Add a demo showing use of sw-btrace, sw-clang-indexer, and sourceweb.

 * The demo uses the "bigint" library from
   https://mattmccutchen.net/bigint/.
Avoid a bug with sw-btrace-to-compile-db that appeared on OpenSUSE 11.4.

 * On OpenSUSE 11.4, the json.loads method produces strings of type "str",
   whereas it produces strings of type "unicode" everywhere else.  I don't
   know why this is -- OpenSUSE 11.4 uses Python 2.7, and I see the
   expected unicode type with:
    - Ubuntu 10.04, Python 2.6.5
    - Mint 13, Python 2.7.3
    - OS X 10.8, Python 2.7.2
    - OpenSUSE 12.2, Python 2.7.3

 * Avoid the problem by forcing the input to be unicode.
Make the sw-btrace-to-compiledb script work on Python 3, too.