This is based on our conversation on Discord and adds a setting for GTK
that allows disabling the GTK single-instance mode.
If this is off, it's possible to start multiple applications from the
same release binary.
Tested like this:
```
$ zig build -Dapp-runtime=gtk -Doptimize=ReleaseFast && ./zig-out/bin/ghostty --gtk-single-instance=false
[... starts new application ...]
```
and
```
$ zig build -Dapp-runtime=gtk -Doptimize=ReleaseFast && ./zig-out/bin/ghostty --gtk-single-instance=true
info: ghostty version=0.1.0-main+42a22893
info: runtime=apprt.Runtime.gtk
info: font_backend=font.main.Backend.fontconfig_freetype
info: dependency harfbuzz=8.0.0
info: dependency fontconfig=21400
info: renderer=renderer.OpenGL
info: libxev backend=main.Backend.io_uring
info(os): LANG is not valid according to libc, will use en_US.UTF-8
info: reading configuration file path=/home/mrnugget/.config/ghostty/config
info(config): default shell source=env value=/usr/bin/zsh
(process:49045): GLib-GIO-WARNING **: 13:55:56.116: Your application did not unregister from D-Bus before destruction. Consider using g_application_run().
[exits]
```
* search for resources dir relative to executing binary on Linux
From Andrew in #241:
This works in all 3 of the possible scenarios I can think of on Linux:
* `zig build` with default prefix into `zig-out`
* `zig build -p ~/local` (my choice when compiling from source)
* ghostty packaged for a linux distribution into /usr/bin and /share
* update README
This just popped into my head. Took me a while to figure out the syntax
a few weeks back, so why not document it here? I don't think it'll
change.
I can change the colors though. What I have here is my gruvbox theme.
Maybe we should use the default colors?
