avro

Sort the docs items by their recency

More recently released versions are at the top.
The value of `weight` is: minus-sign followed by the version without
dots, e.g. 1.12.0 => -1120
The special version `++version++` (meaning "in development") is always
at the top, with weight=-9999

Signed-off-by: Martin Tzvetanov Grigorov <mgrigorov@apache.org>