Update Python bindings to use bson_reader_new_from_data.

Not strictly required for libbson itself, but helps when people go
to build mongo-c-driver since it relies on it to find libbson-1.0.pc

So lets remove it, we don't want to maintain unnecessary stuff.

This adds BSON_HAVE_STDBOOL_H to bson-config.h so that we can easily
include <stdbool.h> when available. The previous check was not ever
getting used by external software because they would also have to
define HAVE_STDBOOL_H, which nobody does. And of course, this causes
inconsistencies in function calls.