Correct some typos across the documentation.

This commit was made thanks to the tool and PR
created by Lajos Veres (vlajos) on github.

PR: https://github.com/apache/httpd/pull/6
Tool: https://github.com/vlajos/misspell_fixer



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1780218 13f79535-47bb-0310-9956-ffa450edef68