Add more features, bug fixes and bugs ;-)

Most notably:
- Reflow is now working. Terminal size will fill the window and
cols/rows will be resized/calculated based on window and font size.
- Added support for different fonts (i.e. bold, italic, bolditalic).
- Enabled blinking characters.
- Adde more tests and caught a few subtle bugs.
- Removed renderer code (which was part of xterm.js) and just
doing naive rendering in terminal.gd, but it seems to perform
a lot faster.

Still not working completely:
- vim (some weirdness going on).
- vttest (more weirdness).

Todo:
- Fix the above.
- Draw the cursor!
- Improve performance. Performance is still not great. The terminal
becomes unusable when running `yes` or `cmatrix -r`.

addons/godot_xterm/fonts/source_code_pro/source_code_pro_regular.tres

@@ -3,5 +3,4 @@
 [ext_resource path="res://addons/godot_xterm/fonts/source_code_pro/source_code_pro_regular.ttf" type="DynamicFontData" id=1]
 
 [resource]
-size = 20
 font_data = ExtResource( 1 )