Please abuse my proto-refactor branch while I'm gone

[Daniel Franke]

Susan and I going to be on vacation in Colorado from July 9-17. While
I'm gone, please pull my proto-refactor branch off of gitlab and abuse
it. If you find bugs, please feel free to commit patches directly to
my branch in my absence. Current status is as follows:

Implemented and successfully smoke-tested:
* Client mode
* Server mode
* Control mode (ntpq)
* Pool mode

Implemented but completely untested (I may tick a few things off this
list before the end of the day):
* Authentication
* Parsing packets which contain extension fields
* Symmetric active/active mode
* Manycast mode
* Rejection of bogus replies
* Proper application of 'restrict' lines

Unimplemented:
* Symmetric passive mode
* Multicast/broadcast client mode
* MS-SNTP
* Interleaved mode (deliberately removed)

Known regressions:
* Missing call to record_raw_stats()
* Some system counters aren't being updated (e.g., sys_newversion,
sys_oldversion)