feat: enable changing the inputHandler of a terminal

Only setting the size of the terminal in characters
and reporting this size is supported.

fix: export TerminalTargetPlatform

fix: only dispose the FocusNodes which TerminalView creates

feat: expose readOnly flag of CustomTextEdit in TerminalView

The TerminalTargetPlatform enum is used for a parameter in the terminal
constructor. Correspond...

SchedulerBinding.instance warning removed

Allow scroll shortcuts

Add TerminalBackend.isReady and connect to Terminal.isReady

Allow changing themes

Allow changing themes without rebuilding the entire terminal and losing
its buffer.

This allows the backend to communicate when it's ready to resize etc.

Don't unconditionally force-scroll to the bottom for any (modifier)
key but only if the user is ...

fixes Issue #82

adds check if the TerminalIsolate has already been started

upgrades Dart for examples
now uses dartssh2

and throws an exception when it is not

add configuration options for keyboard

change interface of ssh.dart example to satisfied new dartssh.

fix assert of scrollController.position

Fixes inverse color text (when background == 0)

assert when start up.

fix example build problem of flutter-windows for new version of flutter.

flutter create.

Fixes ALT + L for a Mac (German Layout)

that means '@' but also triggered "one word forward" (ALT+L)

Fix for occasional unintended multi character input

Feature: Search

This pulls too much noise into the Mocks and isn't really needed (from a functional POV)