Commit GUT directly to the git repo and remove gd-plug as it is no
longer required to install GUT.
Modify GUT to be used by command-line only.
For example:
```
cp test/.gutconfig.ci.json .gutconfig.json
godot --no-window -s addons/gut/gut_cmdln.gd
```
Makes for pretty paths when extending scripts:
`extends "res://addons/godot_xterm/terminal.gd"`
vs.
`extends "res://addons/godot_xterm/nodes/terminal/terminal.gd"`
Currently "res://addons/godot_xterm/pty.gd" is acutally `pty_unix.gd`.
This is okay for now as the PTY node is only supported on Unix
platforms. However, we will need to sort it out when adding Windows
support as part of #25.
Also remove the GDXterm namespace.
- Enable tests for osx.universal platform.
- Export HTML5 (but skip upload as .cast files aren't exported
properly).
- HACK: Use HTML5 export to generate .import directory for tests
This way we don't get an error message even if using
`continue-on-error` set to `true`.
Currently tests only run on X11.64 platform.
But other platforms can be supported with a bit of effort.
Remove default bell sound as it does not play nicely with CI environment
that does not have sound card.
Gut was freezing on some integration tests. It was also entering an
infinite loop after exiting (even after closing Godot and VSCode) which
caused a `godot.log` file in app_userdata to keep growing until my hard
drive was full.
Fresh clones of this repo will need to install Gut using
gd-plug:
```
godot --no-window -s plug.gd install
```
Similar to how git submodules also need to be installed.
