docs: cosmetics: Make example code indentation consistent

Signed-off-by: Diego Biurrun <diego@biurrun.de>
docs: Switch to modern qemu syntax for host port forwarding

Signed-off-by: Diego Biurrun <diego@biurrun.de>
docs: Fix a number of typos and grammar errors

Signed-off-by: Diego Biurrun <diego@biurrun.de>
docs/WritingPlugins: Fix some example code errors

Signed-off-by: Diego Biurrun <diego@biurrun.de>