This commit expands on the prior commits to introduce the concept
of per-window configuration overrides.
Each TermWindow maintains json compatible object value holding
a map of config key -> config value overrides.
When the window notices that the config has changed, the config
file is loaded, the CLI overrides (if any) are applied, and then
finally the per-window overrides, before attempting to coerce
the resultant lua value into a Config object.
This mechanism has some important constraints:
* Only data can be assigned to the overrides. Closures or special
lua userdata object handles are not permitted. This is because
the lifetime of those objects is tied to the lua context in which
they were parsed, which doesn't really exist in the context of
the window.
* Only simple keys are supported for the per-window overrides.
That means that trying to override a very specific field of
a deeply structured value (eg: something like `font_rules[1].italic = false`
isn't able to be expressed in this scheme. Instead, you would
need to assign the entire `font_rules` key. I don't anticipate
this being a common desire at this time; if more advance manipulations
are required, then I have some thoughts on an event where arbitrary
lua modifications can be applied.
The implementation details are fairly straight-forward, but in testing
the two examplary use cases I noticed that some hangovers from
supporting overrides for a couple of font related options meant that the
window-specific config wasn't being honored. I've removed the code that
handled those overrides in favor of the newer more general CLI option
override support, and threaded the config through to the font code.
closes: #469closes: #329
