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`.

test/integration/test_terminal.gd

@@ -100,9 +100,3 @@ func test_csi_position_cursor():
 	parse(parser, '\u001b[1;5H')
 	assert_eq(buffer.calls, [['csi', [1, 5]]])
 	assert_eq(buffer.printed, '')
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