Updates based on feedback from Ruediger and Jeff:

- correct use of "up" and "down" w.r.t. filter chain
- various grammar fixes
- recommend use of apr_brigade_cleanup() in the brigade structure section
- fix use of APR_BRIGADE_INSERT_HEAD in an example
- expand section on use of ap_save_brigade()
- simplify rule regarding fixed processing fixed # of buckets


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@519960 13f79535-47bb-0310-9956-ffa450edef68