Document feature from TS-1125

This closes #153
TS-1570: Minor fix for ats_ip_parse and additional regression tests.
TS-3224: fix problem of ts_lua coredump
TS-1475: fix clang warning
docs: update focused on architecture documentation
[TS-3226]: Move access of read vio inside the mutex to prevent ntodo corruption
update CHANGES
fix minor coverity errors
Fix apidefs.h header guards
Fix typo in epic plugin docs
TS-1461: Update traffic_manager to restart with exponential backoff
Fixing typo in plugin reference documentation

This closes #155
TS-153: "Dynamic" keep-alive timeouts for incoming connections
Updated 5.2.0 release.
Updated with 5.1.2 release as well (I assume it's today :).
docs: add initial content to the performance tuning section
TS-3237: Don't segregate DNS results by port.
TS-3238: remove _res symbol dependency

The global _res symbol from libresolv was ostensibly being used to
get resolver options, but in fact those options were never used.
We can remove our reference to it.
TS-1256: add ink_file_namemax to replace raw pathconf calls
TS-3239: add a new generator plugin

The generator plugin is a server intercept that can generate HTTP
responses according to the specification given in the request URL.