Add human-readable logging infrastructure

[charmoniumQ]

Our record_logger and the CPU timers in #209/#211 are good for computer-readable telemetry. However, we need an infrastructure for data intended to get to a user, such as warnings, error descriptions, and debugging messages.

Perhaps, we should use glog.

• By default, ILLIXR should not print anything except for really critical stuff (why this is considered "good UNIX style")
  • Logs in a loop can use something like glog's LOG_EVERY_N.
• Many of the assert(thing && msg) can be replaced with glog's CHECK(thing) << msg.
  • This permits the message to be a dynamically generated string, like CHECK(thing) << getErrorMessage(msg) which would not work with a raw assert.
  • CHECK is not suppressed by NDEBUG, which has caused us bugs in the past (and pesky [[maybe_unused]] annotations).
    • One can still explicitly reserve a check for debug builds by surrounding the CHECK with #ifndef NDEBUG, as we do already in many places (e.g. common/record_logger.hpp).
• Glog can dump the stacktrace on segfault.
  • We do already have catchsegv. There's not a whole lot of benefit to switching over to glog for that.
• Glog embeds the filename and line number in all logs.
• Perhaps we want to "selectively enable" debug flags for different plugins, as in LLVM. This is the only thing not readily avilable in glog.