INI settings should be on the official docs site from here on forward.
Updated INI Settings (markdown)
Fix formatting
Document APC settings
Documented fact that allowed_exec_cmds only works if whitelist_exec is true
Correct pid file ini setting
Add hhvm.mysql.slow_query_threshold
Document hhvm.xenon.period and hhvm.xenon.force_always_on
Documented hhvm.error_handling.call_user_handler_on_fatals