feat: tea.WithContext ProgramOption to supply a context

WithContext lets you specify a context in which to run the Program.
This is useful if you want to cancel the execution from outside.
When a Program gets cancelled it will exit with an error
ErrProgramKilled.

options.go

@@ -1,6 +1,7 @@
 package tea
 
 import (
+	"context"
 	"io"
 
 	"github.com/muesli/termenv"
@@ -14,6 +15,15 @@ import (
 //	p := NewProgram(model, WithInput(someInput), WithOutput(someOutput))
 type ProgramOption func(*Program)
 
+// WithContext lets you specify a context in which to run the Program. This is
+// useful if you want to cancel the execution from outside. When a Program gets
+// cancelled it will exit with an error ErrProgramKilled.
+func WithContext(ctx context.Context) ProgramOption {
+	return func(p *Program) {
+		p.ctx = ctx
+	}
+}
+
 // WithOutput sets the output which, by default, is stdout. In most cases you
 // won't need to use this.
 func WithOutput(output io.Writer) ProgramOption {