[PATCH 0 of 7] limit_rate improvements

[Maxim Dounin]

Hello!

The following patch series implements various limit_rate and related
improvements, notably:

1. The limit_rate directive was modified to use leaky bucket algorithm,
with limit_rate_after being burst size limit.  Such approach ensures
more precise limiting and better handling of complex traffic patterns.

2. The limit_rate and limit_rate_after directives are now supported in
the mail proxy module.

3. The send_min_rate and client_body_min_rate directives, which
configure minimum transfer rate which needs to be maintained by the
client.

Review and testing appreciated.

--- 
Maxim Dounin