ATS (Apache Traffic Server) JA3 Fingerprint Plugin

General description
--------------------
1. JA3
This plugin looks at all incoming SSL/TLS clientHello and calculates JA3 fingerprint for each client.
It then performs
1) logging JA3 string and its MD5 hash to `ja3_fingerprint.log` in the standard logging directory;
2) appending `X-JA3-Sig` and/or `X-JA3-Raw` headers to upstream request (depending on the config)

The log file format is as follows:

[time] [client IP] [JA3 string] [MD5 Hash]

2. plugin.config
In plugin.config, supply name of the plugin and options
Example: ja3_fingerprint.so --ja3raw --ja3log
Add flag --ja3raw if `X-JA3-Raw` is desired other than only `X-JA3-Sig`.
Add flag --ja3log if local logging in standard logging directory is desired.

3. remap.config
This plugin can also be used as a remap plugin. For each remap rule, add plugin and parameter field. For example:
map http://from.com http://to.com @plugin=ja3_fingerprint.so [@pparam=--ja3raw] [@pparam=--ja3log]

4. Requirement
Won't compile against OpenSSL 1.1.0 due to APIs and opaque structures.
