SIP78 Convert switches to run time options

[Alomir]

#78

This is Part 1, since this is a good place to partition the work, and I've made enough huge PRs recently...

This PR:

• Creates a global Context struct to hold config options
• Reads options from both sipnet.in and the command line, merging them into the Context object (command line has precedence)
• Adds command-line options for a few params as proof of concept
• Updates the help text with this change
• Uses a hash_map (based on uthash, a third-party header file) to manage metadata about context params, including what source the param value comes from
• Adds option to dump the final merged config into a file named <inputfile>.config (e.g., niwot.config)
• Removes namelistinput, as that is superseded by the Context

Part 2 of this task will be to convert the compiler switches that we are keeping as options to run-time args, update the Context and cli for these options, and remove/massage code related to the flags that we are removing or hard-coding on.